Since this thread is as dead as a doornail, I'm here to bring you a guide explaining the thought process and essentials behind many balanced and bulky offensive teams (my favourite archetypes) in the Ubers metagame.
This is in a subjective order of priority by the way. It's the order I always stick to and it of course can differ among Uber players.
*Primal-Groudon counterplay*
Being the undisputed ruler that has the metagame in a stranglehold, it should be crystal clear that any balanced team should seek to counter or at least hard-check Primal Groudon. Since Primal Groudon very often tends to be a team’s Stealth Rock setter, it usually is a good idea to equip your team’s defogger with the tools to retaliate back at Primal Groudon. Other things you should look to cover up in your team is a Pokémon that can consistently tank Precipice Blades, like defensive Arceus forms or Zygarde, and a Pokémon that can take Eruption/Overheat relatively well like Arceus Water or Giratina-O. Packing a ground immunity like Yveltal, Ho-Oh and Mega-Salamence can also prove to be handy when pivoting around Primal Groudon, though they should not be your only checks.
*Xerneas counterplay*
Geomancy Xerneas is the single most restrictive and influential force in the metagame and should be taken very seriously when making any team. Luckily, gen 7 brought us long-awaited reliable Geomancy Xerneas counterplay in the form of Necrozma-DM and Magearna. Packing a specially defensive Necrozma-DM or a Magearna is usually sufficient when looking for ways to keep Xerneas at bay. Any other Pokemon is prone to getting worn down by Xerneas itself (even offensive Necrozma DM). Hence, if you cannot fit either Spd Necrozma DM or Magearna in your team, you'll probably need to take extra measurements. Good options in that case are cores like Primal Groudon + offensive Necrozma DM, Primal Groudon + priority, Ho-Oh + Ferrothorn or a nifty tech like Roar Primal Groudon.
Having said that, Geomancy Xerneas is not the only Xerneas form you'll encounter in battles. Scarf Xerneas is another very prominent set that is used in order to revenge kill a plethora of Pokémon. Thus, if you pack Pokémon that are prone to getting revenge killed by Scarf Xerneas (Zygarde, Marshadow, Yveltal, U-Necrozma), you must include Pokémon that can consistently tank a few Moonblasts like Ho-Oh, Ferrothorn etc.
*Necrozma counterplay*
If you see a Necrozma-DM on the foe’s team, the first thing you should do is scanning the opposing team, because it is mandatory for you to know whether you’re indeed dealing with a pure Necrozma-DM or whether it’ll ultra-burst into U-Necrozma. This is very tricky since both forms have a usage of approximately 50%. Most of the time however, the form and set can be deduced from team preview. A trick I always use is looking for Xerneas checks. If the Necrozma-DM is paired with a sturdy Xerneas check like Magearna or Primal Groudon, the Necrozma-DM most probably is either an offensive Necrozma-DM or a U-Necrozma. If not, it probably is a specially defensive Necrozma-DM.
However, this is not always accurate, so you will usually want to include Pokémon in your team that can take a Sunsteel Strike or Photon Geyser in order to deduce Necrozma’s set. This can be done with several Pokémon, including Arceus-Dark, Arceus-Water, Zygarde and Primal Groudon.
As soon as you have deduced which set you’re dealing with, you have to act accordingly in order to stop them in their tracks. If it is a specially defensive Necrozma-DM, you have to try to force it out with brute strength through double switches (Primal Groudon, Lunala, Yveltal, Primal Kyogre) and make sure it doesn’t Toxic your defensive backbone in order to prevent it from making too much progress. If it is an offensive variant of Necrozma-DM, immediately switch into your check because you may never give it the opportunity to both Sword’s Dance and Rock Polish (except if you have a Sucker Punch Yveltal). Also, since Necrozma-DM is often used to sponge up not very effective attacks even if it doesn’t have defensive investment, another strategy of taking on an offensive Necrozma-DM is wearing it down through repeated attacks like Xerneas’ Moonblast or Arceus Fairy’s Judgment. If you’re dealing with a U-Necrozma, you should try to revenge kill it with a Scarf Xerneas, Scarf/Sucker Punch Yveltal, Marshadow or Mega Gengar. Offensive counterplay is usually a better strategy in dealing with U-Necrozma than defensive counterplay, because simply put, nothing except for Arceus Dark or Lunala can call itself a consistent U-Necrozma check.
*Yveltal counterplay*
Yveltal is a champion when it comes to dismantling your entire team one by one and there really isn't much you can do against it . If you have an Arceus Fairy or Magearna (or the more niche Tyranitar) in your team, you should be safe (however, Yveltal can overcome those with Toxic and LO/Specs Heat Wave and U-turn respectively). If you're not running either Magearna or Arceus Fairy, be prepared for guessing games, double switches and sacrifices since that's the only way you can defeat it. There are many Pokemon that can take at least one attack from Yveltal and retaliate back hard, like Xerneas, Ho-Oh, Kyogre and Defensive Primal Groudon, but they will be damaged in the process, if not severely.
Although Yveltal has a few viable sets, there are two you should absolutely watch out for: Life Orb and Taunt-Toxic. These are the two sets that Yveltal can use to break through an entire team in the right hands and are impossible to abuse. LO Dark Pulse hits nearly everything obscenely hard while LO Oblivion Wing hits hard enough in order to invalidate Xerneas as a hard check. Taunt in combination with LO Oblivion Wing enables it to defeat Support Arceus forms 1v1 while the fourth slot can be used to slot in very strong and utile priority in Sucker Punch or yet another breaking tool in Toxic. The Taunt-Toxic set isn't per se a powerhouse like the LO set, but it still remains a feared set, for it can break through pretty much every single defensive Pokemon in the metagame with a combination of the crippling Toxic, a recovery-denying Taunt, recovery in the form of Roost and a deceptively strong Dark Pulse, all the while providing defensive prowess itself.
Like I said earlier, if you're not running either Magearna or Arceus Fairy, you should be prepared for guessing games, double switches and sacrifices. Since you'll basically be dancing around Yveltal, you'll at least want a Dark resist in order to pivot around Dark Pulse. This is also a must if you have sweepers that are prone to Scarf Yveltal's Foul Play. The most obvious choice for this role is Xerneas, though you could also use Pokemon like Klefki or Arceus Dark.
*Primal Kyogre*
Yes indeed. There are two Primal Kyogre checks, period; Primal Groudon and Ferrothorn. Luckily, Primal Kyogre does not have the best speed, so you can force it out with offensive pressure through the likes of Marshadow, Mega Salamence and U-Necrozma, though they by no means can switch into Primal Kyogre. If you are facing a Primal Kyogre, be very very preservative with your Primal Groudon throughout the game. Losing your Primal Groudon in a Primal Kyogre matchup is a death sentence. It also is a good idea to scout the Primal Kyogre for the physical set since this variant will defeat Primal Groudon 1v1. The best Pokemon to do this is Arceus Water or Ferrothorn, since they will survive anything Primal Kyogre can throw at it at least once. Equip a Primal Groudon, be preservative, and you should be fine.
*A plan around Shadow Tag*
Mega Gengar, Gothitelle and Gothorita. Uber's personal devils. Since this post is about balanced and bulky offensive teams, you are bound to have at least one Pokemon that is trappable by either of these three ominous forces. In a Shadow Tag matchup, try to intimidate your opponent through double switches to your Wallbreakers, pivot and pray you make the right decisions. Completely healthy, I know. You do have another choice though. Notice how those three are weak to Pursuit. Yeah, instead of them trapping you, you can be the one trapping them. It's a lot of fun too. Marshadow is imo the best Pursuit trapper, though Tyranitar works too.
*Zygarde counterplay*
Zygarde is easily checked by any Arceus form with Ice Beam, Arceus Fairy's Judgement and itself (Coil Rest Zygarde is a hard counter to offensive Zygarde) . It can however cripple them all with Glare or KO them with Groundium Z after some chip. The first thing you should do is scout for it's item. If it's Leftovers, feel free to switch directly into your check. If it's not Leftovers, it's probably Groundium Z and in that case, you should bait it out. If you really want to be safe, you may pair your checks with Aromatherapy Xerneas in order to come out of the tussle unscathed.
*Marshadow counterplay*
Although not as threatening to Balance as it is to Offense, Marshadow should always be on your threatlist. Marshadow is usually covered sufficiently with an Arceus form (or the more niche Toxapex), though if you can't fit a Support Arceus form in your team, other Pokemon like Zygarde, Yveltal, Ho-Oh and Salamence can cover up. However, Marshadow can overcome all of these with either Rock Tomb or HP Ice. Arceus forms without too many Def EV points should also be wary of a Bulk Up Soul Stealing 7 Star Strike, but that is a rare set so I don't really think too much about that.
*Lunala counterplay*
Although not as common as other offensive behemoths, Lunala is not a Pokemon to be taken lightly and will massively disrupt your team if you don't take any precautions. From a defensive point of view, the best thing you can do to halt Lunala is setting up your hazards or poisoning it since that will break it's Shadow Shield. A Lunala with a broken Shadow Shield is literally twice as easy to revenge kill than a Lunala with its Shadow Shield intact. There are however a select few Pokemon (LO Yveltal and LO Marshadow) that can revenge kill Lunala through its Shadow Shield so if you have those, chipping Lunala isn't necessarily a must. When facing a Lunala, you shouldn't seek to wall it since it has tremendous damage output, setup options, a very potent STAB move, a killer Z-move and unresisted coverage. However, having a ghost-resist is often a good idea.
*Mega Salamence checks*
Mega Salamence is yet another threat that can rampage through teams with the sheer power of its Aerilate-boosted Double Edge. Since Mega Salamence is very bulky and therefore hard to revenge kill, your best bet is to equip an Arceus form with either Ice Beam, a super effective Judgement or Will-o-Wisp. You could also use a defensive Zygarde to halt its progress. Luckily, Salamence will often wear itself down through Double Edge to the point where a relatively weak attack like Primal Groudon's Rock Tomb will take it out. Regardless, packing a flying-resist is always a good plan, which brings us to...
*Ho-Oh checks*
Although Ho-Oh very often is used defensively, that doesn't mean its LO and Band sets pack less of a punch. A stray offensive Ho-Oh can easily slice your entire defensive backbone apart, so be sure to scout it's set. Defensive Zygarde, Facade Salamence and Arceus Water are some of the sturdiest checks to Ho-Oh. Rock type coverage from Primal Groudon, Marshadow and Arceus forms also frequently catch Ho-Oh off guard. However, the easiest way to keep Ho-Oh in check is to simply lay Stealth Rocks.
*E-Killer checks*
Extreme Killer Arceus is a former shadow of its glory days, but can still wreck havoc if left unchecked. From a defensive point of view, Celesteela and Zygarde are sufficient in order to keep it at bay. If you are able to pack Will-o-Wisp into your Arceus form you should be fine too. From an offensive point of view, Marshadow immediately comes to mind, though be aware of Chople Berry. Will-o-Wisp Mega Gengar can also cripple it for the rest of the game, though it won't come out of the battle unharmed.
*Offensive Arceus counterplay*
Both Sword's Dance and Calm Mind Arceus forms can be seen from time to time in several teams. Arceus Ground in particular is pretty threatening since it can run both Sword's Dance and Calm Mind. Scouting is again the key here. Defensive Zygarde, Charti Berry/Scarf Yveltal with Foul Play and Marshadow are common answers to Sword's Dance forms while Ferrothorn and Ho-Oh hold their own against most Calm Mind Arceus forms.
Other things you should look to cover up in your team are:
Stealth Rock
Defog
Stallbreakers
Toxic-absorber
A plan against Webs
Some other things that are very handy but aren't required:
Aromatherapy/Heal Bell
Spikes
Toxic Spikes
A plan against other forms of Hyper Offense
If you've read all of that, give yourself a pat on your shoulders. You have listened to an hour of my life-story.