Depends on how you define balance and balancing, this is because an effort to balance can often times lead to a watered down game with a generic playstyle. Throughout the history of competitive fighting games, we've had examples of games that were balanced in terms of character viability but did so at the cost of playstyle viability. For example, Vampire Savior is considered to be one of the most balanced fighting games ever made, but most players will admit that this was at the cost of certain playstyles (in favor of all out rushdown). Happily, the system in VS was deep enough for it to be played for years. Then there's Marvel vs. SF which went against form and was actually a Marvel game that was free from almost all forms of bullshit and infinites, but this was at the cost of making it so that almost every character played exactly alike (and had one basic gameplan). Unlike VS, MsH was never considered deep (due in part to how neutered everyone was) and was shunned competitively.
Compare the above to games like MvC2 or 3rd Strike. In the formers case, despite having only 14-16 out of 56 characters considered viable, the fact that multiple playstyles can succeed in tournaments means that, once you get past any character loyalty, you can find a viable team that fits how you play. Either that, or you can build a team around your favorite character and still win (i.e. Megaman/Blackheart/Cable for those MM fans). For 3rd Strike, despite the seeming dominance of a few characters (Yun, Chun), the upper and middle tiers have a decent mix of playstyles and interesting characters (Makoto, Urien, Dudley, Oro, etc.), and the system itself (parries) eases the difficulty of the matchups somewhat.
On a related note, an
informal study done by Maj of SonicHurricane.com shows that the tournament classics, as far as EVO is concerned have more often than not been more about having
a small number of interesting matchups than overall balance (at the cost of interesting matchups).