And the characters that are resistant/immune to "mind control" would just shrug it off and kill them with ease...
My main concern is that someone with that ability set wouldn't last very long. Arty's nearly immune, the overlord probably doesn't even have a normal mind to control, Thinker's character can move past any manipulation before it takes effect, and every other character has a will of iron that lets them shrug it off. In fact, almost all of my characters have some form of anti-telepathy skill or ability, just to highlight the fact that it's nearly useless in arena combat unless it's OP. Even for characters who aren't resistant or immune, it's extremely difficult to call accurate "damage" because we have no baseline to go with. With abilities that have a physical manifestation, we usually have a real world example of the damage they can do so we use that and either scale up or down.
All that said, I'm certainly not against mental powers so long as they're not OP (mind control is still a no, but mental manipulation is a possibility), but unless they are OP they have very limited usefulness and a specialized character isn't going to last long.