Over my years of playing a wide variety of games, I've come around to the opinion that "party balance" is a myth.
So much depends on the individual game/campaign, and the GM communicating with the players (and the players communicating with each other) to make sure they are offering each character an opportunity to shine.
My goal is to do my best to put together tools for groups to put together the game that serves their needs. With an eye toward fairness (and opportunity) rather than focusing on a somewhat nebulous concept of mathematical "balance" as an end in itself.