You missed the entire point of that section.
First of all, Togekiss does not "deal easily" with Tyranitar switch-ins unless you run both Nasty Plot and Aura Sphere (unboosted aura sphere does not come close to killing it), and while those are good moves on Togekiss they're possibly not the best use of those slots depending on the user's team. It's like saying "Infernape doesn't have a problem with vaporeon because it can run run swords dance and close combat", and while this is true not every infernape runs those moves.
And this is discounting the popular ScarfTar, which wrecks Togekiss without a second thought.
More relevantly, those resistances matter because we don't have to base our secondary typing around not being pursuit/u-turn weak, which is definitely a big deal. That way if we decide to give this thing a Psychic secondary typing, which is easily a good idea, we won't have to worry about "crap this core loses to Pursuit". Note that Pursuit is one of the few weaknesses of CeleTran, so let's learn from that...having Togekiss' partner picked off by a quick Pursuit from Scizor or Tyranitar is not very cool.
As far as U-Turn goes, Togekiss has impressive defenses and resists U-Turn, but it definitely will not appreciate it from the likes of CB Scizor (an average of 35% to 4/0 Togekiss, which with SR means it's taking a whopping 60% damage for doing literally nothing).
Much more important is how Fighting's neutrality and key resistances compares to Ground's. Ground brings significant weaknesses to Water and Ice to the table, which means we nearly have to compensate for these with a secondary typing or end up with a pretty crappy core. It is immune to Electric, which is significant, but can't hit common Electric types (Rotom, Zapdos) with its primary STAB. It resists Rock and Bug, but so does Fighting. Flying/Ground have decent offensive synergy, but not nearly as good as Flying/Fighting.
But the most significant part is the easily exploitable weaknesses it brings to the table. Do you know why Machamp seems so damn bulky despite its fairly average defenses (90/80/85, marginally worse than Salamence's 95/80/80)? It's because Fighting's weaknesses are very uncommon attacking types in the metagame , compared to Ground's weaknesses. What this means is that we don't have to give this an inordinate amount of bulk just so it doesn't die immediately to Starmie or Vaporeon, and we don't have to focus our secondary typing on negating those weaknesses. We can instead focus on more offensive stats and more offense-oriented typing, which is fundamentally the point of this core.
Already covered that Togekiss does not "handle" TTar.
As to Blissey...all it's going to do is switch in, Thunderwave you and, upon finding out that you carry Aura Sphere, just go straight to Rotom, who walls and kills you. No one is going to leave in Blissey on an Aura Sphere Togekiss when it's easily walled by several other popular stall members, and Togekiss that don't have Aura Sphere don't stand much chance (Togekiss needs to be at +6 to guarantee the 2hko with Air Slash...). So having a partner who can OHKO Blissey with a +2 STAB Aura Sphere or just a regular Close Combat is valuable. Now, the primary advantage of Ground in this case is that it is immune to paralysis, which is nice. However, it's not going to be doing much back to Blissey. If it's specially based, Earth Power will barely scratch it, and even if it's physical it will need an attack greater than 100 base and Life Orb to guarantee the 2hko on Blissey with Earthquake. That's not very impressive. I'd rather risk Paralysis and at least get boosted Paybacks or whatever instead of being immune to paralysis but being walled by Blissey anyway.
