I do think there would be benefits to removing the choice for healers to either do DPS or heal. I think an elegant solution would be to rework healers so that their heals result in damage. That could be because any healing done to party members also passively damages enemies, or builds up some kind of gauge that eventually deals damage, etc. There are a variety of ways to do it, and I don't think it would be too challenging to make different ones for each class. But removing the moment-to-moment choice between DPS and healing and replacing them with "actually, both" would be an elegant way to solve that conflict. Bonus damage for overhealing your max health party, etc.