Over-usedness is sometimes a good reason for nerfing. Relative balance also differs between game modes and skill level of players. Take IWAY, for example. It wasn't imbalanced at high levels of player skill; the imbalance was lower. Crap IWAY teams could pretty much always defeat other crap teams, which forced the other crap teams to switch to IWAY or lose. Nav's comment proves my point:

[IWAY is] the only build that a PUG without hardcore third party voicechat could run.
Indeed, it was pretty much the only build that a PUG could run. They couldn't win good teams, but they could roll mediocre or bad teams. This resulted in Tombs filled with IWAY teams. It's the very definition of degenerate, or stale, gameplay when 9 out of 10 teams you encounter use the same build.

I didn't mind good IWAYs, the best of them were actually good players and the games were hectic and furious. It's the vast hordes of dung IWAYs that were the problem.