I don't necessarily think it's a problem that hymns get away from concentration, particularly if they're only affecting 1 person. It's a clear differentiation point from spells, and choosing between affecting another person and making the ability difficult to disrupt is a reasonable an interesting trade-off. I think the real issue with +Cha is that it's a huge swing from 1->5 targets, I don't really see an issue with 1-> and extra expenditure for more.
I do take the point that disruption of these abilities in general is lacking. Obviously there's always just "knocking the bard unconscious" but I wouldn't mind another way to turn them off. How about tying it back to the performance choice, and either requiring the bard's target clearly see them or that they produce sound for musical/verbal performances? That gives you the ability to mess with the bard through repositioning to break line of sight or silence, and to limit their targets through blindness/deafness. You can throw in some anti-stealth stuff too for flavor if you like.