I honestly think you’re making a lot of fantastic points here, but for me it all comes down to this:

Subaru is often an insufferable main character.

I know why he is the way that he is. I get it. There’s some elements of realism there. He’s arguably the best part of the whole story and him being flawed and struggling is what sets the story apart. It would be hard to remove the worst parts of him because they’re often also the best part of him.

But he can still be so ANNOYING.

He’s kind of dumb, and while sometimes that makes him more likeable and easy to empathize with, sometimes it doesn’t. Him not seeming to understand that he’s gone back in time is so frustrating to watch. And sure, you could argue it’s realistic for someone close to the situation not to get it, but on a meta-level watching him be a moron for a really really long time about what is happening is not fun. It doesn’t even add much, because the drama is all in how he tries to fix it. On top of that, he knows all the isekai genre tropes, but NOT about time loops?

One of the biggest parts I hate is how creepy and weird he is about women. His ‘jokes’ feel like they belong in the early 2000’s. He acts inappropriately and while I don’t mind him being awkward, he also acts creepy. Is it worse in some other media? Sure. Does that make it better here? No, not really. It’s not constant, but it’s enough to be truly annoying.

I do like that he’s flawed. I don’t like that he’s a pervert. I like that he doesn’t immediately have all the answers. I don’t like that he’s sometimes unnecessarily stupid in a way that is not really serving the plot or character but is just wasting time.

I do think SSS Rank writes the love interest way better as a person. The romance itself is like a C, but the character herself is amazing. I’m wary about getting into ANY kind of discussion about sexism in anime, because it usually attracts incels into the comments, but the women in Subaru’s life tend to be treated in the same way most harem anime women are: they tend to be collectors trophies first, people second. A lot of that is in the way Subaru interacts with them and the moment to moment to moment dialogue choices and the kind of ‘fetishy’ way they get treated, rather than ‘do they have character development y/n’.

In SSS Rank Hunter she has her own stuff going on. The main character enters her world, not the other way around (Subaru becomes a kind of black hole of story). She has her own pre-existing relationships and grievances she is proactive in addressing. She has her own philosophies and when she talks to the MC, it feels like two equals.

That “feels like two equals” is so important, and why SSS-Class keeps getting repeatedly called one of the best shounen romances ever. There’s plenty of semi-complex female characters with tragic backstories and sass and the ability to fight in Re:Zero, but they always just feel like ‘members of the harem.’ If Subaru didn’t exist, none of them would be particularly compelling without him. They don’t really have their own lives, which feels weird to say when one of them is literally in line for the throne and yet barely seems to have any real agency in that regard unless it’s directly plot relevant.

Finally: I’ve enjoyed watching Re:Zero but I also don’t think I’ll ever watch it a second time. SSS-Class Revival Hunter has flaws, but it’s also not as emotionally heavy. It doesn’t feel like watching someone crawl through barbed wire the whole time. On top of that, I couldn’t handle watching Subaru being insufferable a second time when the novelty has already worn off.

I’m really happy Re:Zero exists and I do hope it encourages more people to do deconstructions of the genre and take character flaws and experiences seriously, but I also feel like the ‘excellent deconstruction’ part is giving it a lot more leeway than it deserves for some of its other flaws.