Xerneas isn't the only one - all Pokémon you can only catch once have three perfect IVs this gen, so Yveltal, Mewtwo and the legendary birds too.

I don't use Blaziken, but the ones I've seen all die very fast regardless of who uses them. I really don't get its placement in Ubers >> Talonflame laughs at that thing's face.

Scizor is pretty awesome though, yessh.