One of the things QA and testing does is balance the game. Anything that has the potential to imbalance it is tweaked so that it no longer does. Of course, the more complex the system, the more difficult it is to balance (which is why some configurations of character seem overpowered). However, there is still a big effort to limit imbalance. Overpowered skills deliberately added isn't something I'd like to see. It's far better to have players discover ways to make their character as powerful as they can be based on a combination of all the character's attributes (and their own ability to learn the game mechanics, of course).
That's not to say that an imbalanced game in some minor respects is a broken one. Many players have discovered specific combos in games that give them an edge yet the game remains perfectly playable by everyone, and enjoyable to boot.
