Did you read my post properly? I chose Rock as a typing because it is the strongest offensive complement to Togekiss that there is AND because it is countered by the very Pokemon that Togekiss loves to deal with - bulky Ground-types.
Sure, you had some very good reasons to pick Rock. I'm just pointing out that there are six very good reasons not to pick Rock, too, in uncovered or shared weaknesses.
Now, this definitely doesn't mean I'm disagreeing with your points. But to bring the discussion forward, I'm mentioning new points that you didn't get around to. Overall I think that the defensive problems of Rock are more severe than the advantages it brings in attack.
And on the subject of Ground - Resisting two thirds of weaknesses good, shared weakness very, very bad. And to Ice-type moves, of all things.
Actually, Togekiss can take Ice attacks quite well. Firstly, they're usually Special moves, and Togekiss has great special defense. Secondly, most of the pokemon using Ice attacks don't get STAB. So it's not as much of a problem as Electric or Rock.
We should really be focusing on arguments that take the symbiosis of the relationship into account here [...] The primary type should be able to give a mutual benefit to both parties.
Example: Ground:
Defensively, Ground is immune to Electric and resistant to Rock - Togekiss' two most important weaknesses. On the other hand, Togekiss is resistant to Grass (which hits Ground hard) and neutral to Water. The only problem is Ice... but as I said, Togekiss can cope with ice, and there area always secondary types to fix that.
Offensively, Ground is an amazing attack to get STAB on. It will take out Electrics and Rocks, which both pose huge threats to Togekiss. It also wrecks Steels, which Togekiss otherwise has no way of taking down. Meanwhile Togekiss can combine Air Slash, flinchhax and Roost to take down... well, everything that
isn't Electric, Rock or Steel. That looks like some pretty good synergy to me.
But wait, it gets better! Because Togekiss has to go first to flinch, it can't take paralysis. Lo and behold, Ground pokemon are immune to Thunder Wave.
Basically, there's lots of back-and-forth going on here. Still, Ground is far from the only option... you just have to read the rest of the thread to see that.
What does Steel do for Togekiss that it doesn't do for Zapdos?
Clearly, Zapdos has one of the best part-flying typings with Flying's weakness to Electric and Electric's weakness to Ground both mitigated. It's true that the only typing advantage that Togekiss has over it is the Ghost Immunity.
That gives us two choices. One is to pick a primary typing for CaP11 which is weak to Ghost... Ghost or Psychic. But the other is simply to
make choices later which stop Zapdos from working so well with CaP11. This is only the first stage of the process, after all. Making a pokemon which spreads and benefits from Paralysis, and is a special attacker to make use of Togekiss' Nasty Plots, would do a lot to move the focus away from Zapdos.
petrie, while I do support Psychic, I think everyone'd like to know how Togekiss is supposed to deal with the Ghost once he switches in, because depending on the Ghost being choiced is a poor idea.
It's quite possible that Togekiss' movesets would change in response to CaP11. Indeed, it would be a bit odd if they
didn't. If CaP11 is Psychic, then Togekiss could start running Shadow Ball more often, and Ghosts would be (a bit) less of a problem.