Honestly, not at all. I'd say if one of the zombie factions *could* be considered OP (and it's NOT) it's the Brainy faction. They have some of the best zombie cards and tricks, but even they aren't OP as far as I'm concerned. I feel comfortable playing against any heroes and any decks.
Hearty has some good cards, like all 10 factions (both P and Z), but not OP by any means. Weedspray is a good card. But nothing too scary. You just have to know when to play around it when facing a hearty zombie opponent. But it sucks against a lot of control plant decks too.
