I agree that all cards cannot and should not be perfectly balanced.
Currently, there are quite a few cards in the game that are very powerful (Graboid, Cremation, Supernova) but are not incredibly game-breaking. The only card that is that broken right now is Fractal, simply because it allows you to spam any type of creature you wish (Namely quanta-generating ones, so that you can then Fractal Dragons or some other good attacker) so that it's impossible to control without numerous renewable control sources (EE, Otyugh), Fire Buckler, or enough mass control to take care of your targets.
So, Fractal needs to be fixed.