Forgive me if I misunderstood that statement, but isn't that approach a bit detrimental to the femdom narrative?
An "organic playthrough" refers to the player playing to their tastes rather than external concerns (bug testing, exploits, completism, etc.). It doesn't really relate to the rest of your post, though.
Your critique boils down to finding Ethan's ability to bounce back from mind breaks unbelievable, which is fine, but that line is somewhat arbitrary. Why can he walk away from the mind-melting QTEs and loss scenes? Why did he risk dojo secrets for a footjob from Yvonne? Why doesn't Scarlett just immediately put him in a cage?
My answer (which you're welcome to disregard; I'm explaining how the story is written, not telling you how to interpret it) is that Ethan is simply very malleable. Despite his ambitions, he is not a hero (yet), just an apprentice. His morals are naive and simplistic. His sexuality is ambiguous.
"Giving up on himself, betraying everything he stands for, and placing his entire existence in enemy hands" is thus much less significant for him than eg. Roman or even someone like Gerald.
This makes it easy for the women to manipulate him. Give him a shoe to sniff and it's not hard convincing him to play puppy. But conversely: show him the dojo photo or say "Rose" and he's right back in hero-mode. More severe manipulations take longer to recover from and leave irrevocable influences, but don't change his fundamental (lack of) nature.
Note how a crux of the current Bad End is that Ethan can truly no longer proceed through the tower. As for the rest, they all have him in their clutches but explicitly choose to let him go for various reasons. Perhaps you find those reasons flimsy, but they are there (and have planned payoffs etc.).
Ultimately, the ideal point to end the story is a matter of taste. One could argue that the women should break Ethan much more quickly than they do, or that the current arc-ends should have finished him (as you do). My stance is that it's more fun to find something even deeper of his to break and corrupt once the obvious (dojo stuff, etc.) is stripped away, and that letting him run "free" (or is he?) in the meantime adds significantly to the eventual fall.
If you prefer to imagine your MC as more initially determined, but only able to endure one real break (rather than the pendulum-like effect I'm trying to write), then you're of course welcome to play that way. Just understand that it's (slightly) contrary to the intended narrative and may cause some hiccups for you as a result.
As for "damage to his physical and mental health" in a gameplay sense, I've explained elsewhere while this idea doesn't really work in practice, but there will continue to be content unlocked by having particular Mistresses (eg. puppy gear, scene variations, etc.).
