As someone who played BP teams recently in huge amount from Jan to Feb and reach pretty high up the ladder, I would like to say this.
Fully dedicated BP teams rarely have enough rooms to fit any move they want. It's usually this, Stored Power to sweep and a fairy/alternate move for dark types.
Scolipede needs to run enough EV into speed to outspeed trick timid rotoms, mental herb is also more favourable than leftovers.
Vaporean is used because it is a great physical wall and has access to Roar. Roar is needed to stop set up sweeper. Encore from either or both Mr. Mime and Smeargle are good too because they stop passive boosters right in their tracks. Thing likes Calm Mind, Cosmic Powder, Swords dance, Nasty Plot etc. You'll be able to use to Spore, Ingrain, Calm Mind meanwhile. Like to add that people usually switch in with Aegislash against Mr Mime and shadow ball is the most common move used and it's especially great if you bp to smeargle and encore it.
So what if they use speed boosting moves? Because you cannot permanent-encore if they end up faster than you, that's when you BP to Vaporean and roar them out if you can't take them atm ( very little boost ). If you can kill them directly, then by all means BP to Espeon / sweeper instead.
Mr.Mime has immunity to Dragon Tail as well as Perish Song and Roar because of its ability. Not to mention, it is a fast pokemon, so if you tried to set up in its face, you'll likely get encore.
You'll need a lot of substitutes within the team, stopping status hazard is important but most importantly, you need to deal with crits.
BP teams cannot afford to trade blows, so they have to set up substitute first to prevent ohko. During this time, even if they are well/fully boosted, without a substitute they have that 10% chance to lose if they get ohko. My Espeon with 4 CM under his belt just got ohko at full health by a Focus Slash Galvantula. Nothing I can do here. Crits and secondary effects by nature work against dedicated BP team and you just need to take one out, the momentum is gone and is very hard to build it up again.
What are the great threats against BP team?
I would say it's less about taunters/trick and WW/Roar users. Yes, random pokemons with taunt/trick that you didn't expect hurts but most people run them in a very predictable ways. Fast pokemons or on walls. Ingrain works against WW/Roar, even without, you have Espeon and Mr.Mime. WW is more a trouble than Roar. The move Curse is a default win most of the time.
Be very aggressive right at the start. Most BP team users know by experience how much boost they need to survive physical/special onslaught. Talonflame, Mega Pinsir. Volcarona are nice picks.