Diablo is not, has never, and will never be a game like wow where "balance" is integral. Fuck off with that shit. The game is about killing monsters for loot.
Now, at exceedingly higher difficulties when playing for greater rewards, you're going to get funneled into a couple of different viable builds due to what's the most efficient, survivable, etc.
You haz a sad because you have to play a WW barb or a CM/archon wizard to beat bosses/elites on MP 10 instead of your own wonderfully unique, beautiful snowflake of a build that you thought up ALL ON YOUR OWN? Oh you poor fucking baby.