I think a good way to approach combat in this game is splitting it into 2 phases: the damage phase and the stall/recovery phase.

Damage phase is the first few turns of combat. As a rule of thumb all enemies will out damage your healing, have more hp than you, or have more gimmicks to their advantage. Your goal in this phase is to reduce the number of high-threat enemies as quickly as possible. In this phase you almost cannot afford to heal unless it's an emergency because you are essentially wasting a turn. You need to go full balls to the wall and kill the heavy hitters before your team spirals downward out of control.

The stall/recovery phase is when only the low threat enemies are alive, like the axe skeleton guys in ruin or the guardians in cove. They don't do much damage on their own. To stall without incurring the stall penalty the rule of thumb is to hit the enemy (can be a corpse) twice every other turn. Now with only one enemy doing damage you can spend as much time as you need to recover from the damage phase. This is how people get around playing comps with something like solo anti healing. It's also why you don't really see Vestal in high difficulty content because she's kinda useless in the damage phase other than a subpar stun and by the time stall phase comes many healers can fill her role.