Note this is MrBeast doing it to himself: https://www.youtube.com/watch?v=K_CbgLpvH9E
I think that changes the ethics a bit. If he decides to potentially psychologically torment himself for his channel, I don't think it's a big deal that he didn't give himself a mental health evaluation beforehand.
(I'm aware he has a similar video with random contestants as well. But either way, I think this particular criticism is a little too hand-wringy. It's not being forced upon anyone and they can leave at any time.)
IMO the biggest issue is the allegation he rigs some of the game shows. That's definitely unethical.