I think Shin Megami Tensei actually solves this with their capturing system, which is really more of a negotiating system. At any time during a battle, you can talk to an enemy demon and ask them to join you. They may request money, items, health/MP or require you to answer questions correctly in order to join you. It’s neat since it has some risk/reward since you can keep plying them with more resources or you can say they’ve gotten enough and push them to join.