Your comments helped me here. I was literally about to ask if the dev rebalanced the game or added some form of difficulty options to give the player a fighting chance. But after reading your comment it sounds like they didn't.
The game's neat and all, and it's honestly the only one of its kind that I know of, but dear god did it take forever to do anything the last time I gave the game an honest try.
In the 1.0 update the healers were the biggest issue because they'd infinitely heal both their friends and themselves. In addition to that they'd sometimes decide that 80% HP was enough to heal an ally and give them something like 35 overhealth depending on the level of the healer. You literally could not kill them without breaking them. At the time there was no punishment for it so it was the ONLY way to kill 3-stacked healers without bashing your head off of your desk for two hours per fight because with my luck EVERY fight was against 3 healers.
Then 1.1 came around which rebalanced a lot of the game. I think in 1.1 when you drain and stun I think the chances/power goes up each time you target the same target. But the enemies get that buff too so each time they drain you it goes up by like 5% which just results in a back and forth until you accidentally break an enemy. Which is bad now and you actively get punished for it with an ultra nightmare difficulty superboss if you do it to the bosses of the game and some other stuff if you do it to the basic enemies.
I barely even played 1.1 because it just felt like more of the same where you HAD to break enemies to win fights but now you got your balls crushed for it as punishment. Stuns were also super unreliable as it was a 50% chance that'd decrease if the enemy was higher level and increase if you were a higher level. There's some gear in the shop that is pretty much REQUIRED to win any fight, specifically the item that gives your character TWO TURNS as that means double stun, heal, or drain which is absolutely necessary to outscale the enemies. The problem is, it's legendary and you pretty much need 3 of them.
I'm still gonna try 1.2 but this does not give me high hopes that I'll enjoy it. So far it DOES seem like overhealth was mostly solved as everyone has a cap of 3x their max health.