Bard song "Battle Voice" -- doesnt affect all party members bug?

[Fannah]

As the purpose of the game is not to solo content, you shouldn't feel like you've learnt a useless skill ^^
Remember "Raise" sucks for solo content as well But I don't believe any healer is like "erf it sucks for solo content".
Same for Aggro Stance and Taunts for tanks, it's useless in solo content too.

Maybe they don't want to see a Bard singing loudly to be heard only by himself in solo content and would look socially awkward (about RP of course, and don't worry, it's all about numbers, they could allow Battle Voice to work on the Bard itself and lower another skill dmg so the overall DPS designers want it to deal is approximately the same).