I can't remember the last time I fought a bard who could sing fiend who didn't attempt to fiend me. Even when I played my drow axe spec bards tried to fiend me.

When I played my fire ap, bards travelled from all over Thera just to enjoy a go at fiending me (and the one bard who killed me was a bard who couldn't sing fiend).

If I was to make a change to fiend, it would be this:

Make fiend a song that can only be used against groups, not against individuals. You could justify this by saying it feeds on mass hysteria.