I'd like to expand upon something I posted above in direct response to these two posts. In concept, you're right. One must prepare for threats, that's how the metagame works. But there's a major difference between something that's threatening enough to require planning, and something that's so threatening that it all nearly invalidates anything it beats. I'll use Zapdos as an example, because it's a top threat and Upstart mentioned it. You've got to plan for Zapdos. It will tear you a new one if you don't. But just because something is beaten by Zapdos doesn't mean that it isn't as good. The fact that Zapdos shuts down Crobat all but entirely doesn't hurt the latter's usage at all. Even though Zapdos and Raikou are everywhere, Crobat still sees a high amount of usage (by good players might I add). However, this isn't so with Chansey. If you have a Zapdos that lacks Volt Switch versus a Chansey, it's dead weight. You're shaving off 25% health for nothing. Even with Volt Switch, hazard damage and lack of recovery hurt Zapdos. It'd be ok (spec zappy is good) if Zapdos could do
something, but it can't. All it's doing is keeping momentum, and you're most likely about to lose it again because there are several Pokemon that have Fighters on lock down. CM Raikou is a thing of the past. Azelf can't do anything but set up Rocks really. Mixed PZ (use it) is the only Porygon-Z worth using, and even that can't break Chansey if it gets a Special Attack boost (thankfully everyone runs that 4 in SpD).
Yeah, stuff like Sub Seed Shaymin and mixed PZ beat Chansey. Chansey is definitely beatable. But honestly, the strain on teambuilding is too strong. Good Pokemon become bad solely
because they are bad against Chansey. If they were borderline and Chansey pushed them over the edge, it'd be one thing. But great Pokemon will become worse team picks because of one Pokemon. Not the metagame as whole pushing these Pokemon down, one Pokemon. Actually, it kind of is the metagame because Chansey is the metagame. Pokemon and sets live and die by Chansey (who used Sub Seed Shaymin before Chansey?), and that kind of metagame control exerted by one Pokemon is undesirable. It's not Rayquaza, it won't 6-0 you. But it works it's way into the metagame, controlling it to a level one Pokemon shouldn't. It's not lazy teambuilding, its painful teambuilding where every member of your team is picked with one, single, solitary Pokemon in mind. If that kind of teambuilding and metagame appeal to you, I'll respect your opinion. But it doesn't to me and a large number of other players. In cases of opinion like this, it has to be majority rules. If the majority turn out to be with Chansey, I'll put up with it, but it doesn't seem like it.
imo Upstart, the cry against Chansey was in no way "not giving it a fair trial." A large number of users had played with it, it had already gotten trial enough to bitch about. Not trial enough to ban, as metagame's change, but trial enough to bitch about and call for a real trial (which is what it's getting) automatically. Also, FlareBlitz has some great arguments
about why Chansey decreases skill, and the last bit about balance and diversity echo's what I'm arguing.