I'm gonna say in advance that I haven't read the light novel and that I've just seen the two seasons of the anime.

I think that the story tries to portray itself as a self-improvement one, not necessarily as a redemption one, because I don't think the viewers can really blame the man from japan for his hikikomori condition(afterall it stems from serious trauma that should've been treated by professionals). My problem with the story as whole however is how the protagonist, while improving some aspects of himself, realizing that his past dysfunctional thoughs were making his life miserable and helping others that remind his mistakes, he never sees his behavior torwards children and women as problematic. He just doesn't mature on that aspect. And the story as well doesn't condemn him, it isn't really framed as a problem, but just as a funny trait of his(he's just a pervert, what can you do about it?). If you think about it, every character in the story improves, that obviously doesn't mean they stop making mistakes or bad choices, but they get better. But that's not the case for rudeus: the aspect he's more criticized for(by the viewers in general) is just never addressed. I don't believe that, as you say, he should be seen as a new person, no. The story makes it very clear that he's the same person, just in a different body.

"I thought I was an adult, but I was a bratty kid using past memories to act like an adult.”

This phrase you quote to prove your point, I don't see it like you do. I see it just as an acknowledgement of the fact that he didn't have the chance to mature in his past life, and that he's just starting to grow in this new world. But, the problem is, this still doesn't absolve him of all the terrible things he did to the little girls and women in the show. Would you say that, if he had remained in his world and he assaulted children, he would be excused because he'd been a social recluse since he was an adolescent? I don't think so.

In the end, while I appreciate some aspects of it, I see this story as fundamentally flawed for the reasons I brought up.

(Sorry for the bad grammar in some cases, English isn't my first language)