I think balance is important, but don't think the RAW themselves define balance. Further, I think you can only balance a game so far before the mere "noise" of campaign variations makes nitpicky balancing efforts pointless.
AFAIAC, there are two primary forms of balance:
1) PC vs. PC: Balance considerations of these sorts minimize player jealousy and spotlight stealing, and help mantain variety in the game by ensuring that there are a variety of viable options for any character design choice the players may make. If a certain feat or class comes along that is clearly the best, one should not be surprised when every sensible player takes that option.
2) PC vs. GM: Balance considerations of this choice help to ensure that it is not too difficult for the GM to challenge the party without negative consequences (e.g., excessive work on the GMs part, unbeleivable "metagaming" NPC behavior, killing half the party while leaving the rest unscratched.)