I get what you mean but trauma really really fucks up your brain. People you think are being "soft" or "doormats" are just incapable of or severely struggle with standing up for themselves. It's easier to defend others than yourself because you grew up being put down constantly. He lacks self respect and that's not HIS fault, it's literally the fault of his sister.
You're correct that trauma will fuck a person up, yes. But even at that point - as someone of his standing, with the goals he has, and the
six predecessors in his head who are feeding him their combined experience and ego - he
needs to learn to actually grow a spine.
Maybe it's the pacing of it, or something, that's the issue. But even if in this moment it's understandable that he might lay down and take the insults and do nothing to defend himself, it's a clear indicator that such behavior
needs to have a expiration date, and the sooner the better.
The more he lets the world walk over him, and the more he just stands there and makes
no effort to even try to change himself for the better, the greater the chance he'll just lose all over again to his sister - and it won't be just him that suffers, this time, now that he's wrapping others up in his problems.
Which is my greater point. I can excuse a conditioned lack of self-worth, but the amount of time this series has been running, versus the clear incongruent amount of
in-story time we've gotten, makes it feel like he should be further along on his "self-improvement journey" than he actually is, creating this dissonance of where he
seemingly should be, and where he actually is.
That, coupled with what he's already accomplished, makes him sorta come across as that sort of spineless MC that
is often portrayed in series, without any of the argument of a horrific childhood to justify it.
All that to say - he needs to stop with it quick,
if only for the sake of those he now cares about it.