This is the end.

[Miste]

Says the person that feels they can play how they want regardless of how it affects the party.

Well just going why what he said since we don't know both sides like you said but...he said they immediately attacked him over having ballad up calling him worthless etc. That is not the way to deal with things. You said "he feels he can play however he wants regardless of how it affects the party" but that is assuming he actually knows what is best and isn't doing optimal on purpose. He has no healers leveled so I am assuming he doesn't know that most healers don't need ballad in dungeons and they manage their own MP.

People in general have to start being more inquisitive instead of accusing. If someone is doing something not optimal you could just ask why and casually explain why they would be better off doing something else instead of not asking and just break out into "omg u r sooo stoopid for doing that, u so worthless". It IS possible the person just doesn't know or forgot.

That is not necessarily how things went down but I've had it happen to me. I leveled bard but I rarely play it so I forget things all the time. I've had both sides of people. Ones that ask me to use a song cause I am forgetting which I am glad they reminded me. Or the ones who yell at me "you $%$%#$#& suck bard" cause I am not doing what they want or what they think is best. All they had to do was ask me or let me know what would help them without resorting to raging.

Also lots of players are different. Some might want bards to do one thing during specific encounters while another would prefer you did something else. No one will ever know for sure what you want unless you ask first.

TL;DR - You can't just assume everyone else knows everything you do.

OP don't quit over this. It isn't worth it and you'll never see those players again likely.