The problem with current bard design is that its by far the easiest dps to play effectively, which is fine however alot of the fights at endgame are punishing to classes that require positioning, have limited range or cast time attacks, those classes will struggle to keep up with a bard that have 100% uptime.

However in coil the other dps can finally get close to 100% dps uptime, however bard's remain the safest dps choice for most guild progressing into endgame and alot of guilds run 2 or even 3 bards and this is where the second design problem lies, bards stack up extremely well, piety bards can keep tp or mana songs rolling endlessly (or close to) by chaining songs, this tactic trivialise alot of the endgame content (or at least severely lower the skillcap needed to beat the boss).

My suggestion would be to put a debuff on anyone that gets a bard song on them for 2 minutes, when you are debuffed you cannot benefit from any bard songs until the debuff is gone.