Besides, SPIKY SHIELD then swap. Turns Acrobatics against him, then gets to tag out.
Honestly, and it's been said before, listing random Pokemon that can beat him is very, very counter productive to any sort of conversation. He has no place fighting Greninja. There is no reason to mention that a random Greninja set can beat him. That does not make him bad that he cannot beat Greninja with Ice Beam or Acrobatics (of all things). Tyranitar is walled by a few choice things, and is forced to switch. That does not detract from the many things Ttar does right.
Chesnaught is a physical tank, with a good defensive typing and surprisingly decent offensive one. He has a workable movepool, and has access to both Spikes and a healing move, an ability that allows him to neutralize quite a few attacks, lending him great switch-ins, and a pretty good signature ability.
He also has many weaknesses. 4x weak to Flying, weakness to the new Fairy, can't take special attacks, slow as dirt (but not slow enough to take advantage of) and the biggest issue, competition. He has to compete with Ferrothorn (and his 4x Fire weak), along with a host of other defensive pokes that I don't quite feel like bringing up.
Some may feel that he might go out like Torterra, but that may not be true (it might be, we'll see). Mind you, Torterra does a lot right, but what he does wrong makes him suffer, and he offers nothing unique, unlike Chesnaught. He can stop a few attacks solid, make a few more invalid, and is able to do his job. He's a niche Pokemon. He can most certainly work in OU, though he may not be everyone's first choice. Many UU pokes are like that.
I most certainly don't have everything, I may be off on a few things, and I am not the best battler, but correct me if I'm wrong, this is the best way to evaluate a mon. Saying (paraphrased) "it sucks because it's has a 4X weakness (since apparently many pokes don't), and there are pokes that can beat it every time (so it's not an uber, then).
If it were a physical wall weak to common physical attacks, then yeah (like a Fire/Flying wall). But saying that a physical tank is weak to a mainly special sweeper is...weird.
Sorry for the wall-o-text.
EDIT: Sorry, Nykheros, I misread your post, you weren't stating that Chesnaught is bad because it can't beat Greninja at all. Still, there were others making similar posts, so I guess the point stands with them instead.