I’m not seeing what the issue is. You can not give a shit about the romantic subtext between the two characters, but it didn’t really prevent nor negatively affect the natural progression of the story. It was a big part of the story but it didn’t overshadow the other things that were happening. In fact, without the romantic subtext, I doubt the story would have progressed the same way from part 1 onwards, since that’s where the implications began. It likely would very much not be the same story if Sandalphon didn’t become popular enough to warrant it becoming a trilogy.

I’m going to go ahead and take a shot in the dark and assume you mean the romantic subtext between Lucifer and Sandalphon since I don’t remember seeing any other characters in the story that had any romantic subtext other than Belial’s one-sided love for Lucilius. The romantic subtext between Lucifer and Sandalphon was the heart of the WMTSB trilogy because Sandalphon became the heart of the story. Not only that, but Sandalphon’s feelings for Lucifer is what mostly made him a sympathetic character to begin with. If we went on him just being pissy because he was a substitute for Lucifer, a lot of people can say despite his popularity that that aspect of his character was wangsty and not something they could relate to. But a lot of us can relate to losing someone we love dearly, whether it be romantically or platonically. Or in a familiar sense if you’re one of the people that claim it can be read that way. That’s what made people sympathize with him enough for it to be justifiable reason to want him on our team, as FKHR intended.

The romantic subtext between them was not in your face, which is why some people can claim it’s platonic. While it can mostly be read as romantic, It can also be read as a deeply rooted bond between two people (One of whom believes he and other primals are incapable of loving others despite Sandalphon being Sandalphon) who had serious communication issues and maybe come to understand each other by the end of the story. Lucifer barely appears in the events and he’s mainly only mentioned in passing, but when he is mentioned or does appear it’s not always Sandalphon being very evidently smitten - It’s him and others describing who Lucifer was before he died, since we don’t get to see much of it outside of a few flash backs. From Paradise Lost onwards it turns into a story of self acceptance and learning to become more than what you are - not just about Lucifer and Sandalphon’s relationship, but that aspects never fails to be a big part of why the story progressed in the way it did. Sandalphon needed motivation to become the Supreme Primarch and to defeat Lucilius’ legacy and he got it.

As another point, Sandalphon’s feelings for Lucifer were supposed to parallel Belial’s feelings for Lucilius. Notice how Lucifer and Lucilius look and sound the same (Until Lucilius gets his body and sounds like a smoker). Belial and Sandalphon also look very similar, too. They both love their respective Lucifaces but Sandalphon and Lucifer’s love is reciprocal and wholesome while Belial and Lucilius’ is one sided and corrupted due to both characters being unambiguously villainous. Belial’s romantic subtext is very much important context to Lucifer and Sandalphon’s relationship as well (Lucifer even parallels what Belial says in the Garden scene near the end of 000) so it’s interesting that you accept one but think the other is unnecessary. Sandalphon is also the only reason why Belial exists to begin with so that says something as well.

I do admit that conversation between Lucio and Sandalphon in God’s Reverie was a little extra, but I felt like it was Cygames reaffirming to the fans that just because Lucifer is dead (For now) it doesn’t mean Sandalphon will ever stop caring about him which I did appreciate. Also, Lucio being a canon Lucisan shipper is pretty funny and fitting.

If 000 was meant to be the end of that arc, it would be weird to end it without any closure for Lucifer and Sandalphon, or any mentioned of their relationship. Readers needed the other events for context about why Sandalphon is so fixated on Lucifer by 000 anyway.

I don’t agree on the sexuality aspect. There are no implications of any sort of sexuality between Lucifer and Sandalphon. They’re just two primals that just happen to present and identity as male that care for each other. To me, their relationship seems pure, Sandalphon going all psycho world-destroyer to get Lucifer’s attention aside since it had less to do with his relationship with Lucifer and more to do with 2 thousand years of being alone with only his self loathing.

It’s okay to say you don’t care for the romantic subtext, but to say if it was removed nothing would change is dishonest. The whole story would be different especially since again, some people read those same lines as platonic, so that would mean removing those “platonic” lines as well and leaving gaps in the story on why Sandalphon would care about Lucifer enough to enact revenge on the people who killed him.

I think Lucilius being a whack fight was justified since he later comes back as a top tier raid boss later with a whole weapon series attached to him.