Worse than Sesshomaru grooming a child?
I mean objectively, SasuSaku is probably still not as bad as even Light x Misa since Light actively despises Misa whereas Sasuke is just neglectful.
I think it's a mistake to have intermixed different reasons for dislike.
SasuSaku is just one of the most horrendously written pairings I've ever seen and I hate it because it was a severe detriment to the series any time it took center stage. This was meant to be a straightforward love story, but it doesn't inspire emotions of affection or happiness because these characters actual relationship is so horribly hollow and performative.
LightMisa is problematic in the greater scope of how the author writes women, but is otherwise a depicted as an unhealthy relationship that serves the story (not only does Light manipulate Misa for her affection, it also shows a different side of him when he loses his memory, ei incorperating the relationship into the intellectual shadow game that is the story of Deathnote). It's well written in that sense and has no detriment to the story unless you just categorically find misa annoying, which maybe is fair, but if that's the case, I wouldn't say you have a problem with the pairing, just Misa's character presentation. But their disturbing relationship pretty much pulls off it's intended effect, to discomfort you to some extent.
Sess-Rin on the other hand is purely problematic without any actual story relevance. Which is to say, it happens during a time skip, so we effectively have no story reference for it happening, we just see the consequences of it in the twins and we can only really disapprove of it in the general sense, like how you may disapprove of any murders Sess did of human beings when before he met Rin. Yeah, it's not good thing, but you're not going to react to it as a story element the way you do SasuSaku or LightMisa that plays out as your watching and has actual narrative impact. It's just a thing that happened that we in the real world disapprove of.
So you may hate SasuSaku because it's just badly written, you may hate LightMisa just because of superficial displeasures like Misa's voice or cutesy attitude, and you may hate Sess-RIn for non-diegetic reasons of how it permits tacitly condones the pedophilic subculture within their audience. Some of those might overlap and I might have missed a few ways, but those are honestly all categorically different experiences for me and I don't really know how to rank "I do not care about these characters but I socially disapprove of their union" vs "I am super invested in the story and these characters, but their relationship is in no way believable and causes major pacing issues and story beat problems"
