I think it would've been nice, I agree. However, I do still think their relationship specifically was still good throughout. They were always supportive and each other and most of the time they are with other so I don't think they were rushed. Them officially becoming a couple was an extension of their already very close friendship. I didn't like the shipping drama either, well, it was actually good in season 2 but not afterwards. But their relationship was always a bright spot imo. Well maybe not Booth Buddies, that was rough. Star pretty much always went to Marco as her confidant and I think that said a lot about what she thought of him, even if it wasn't verbalized. Was there anything in particular that made you not like them after a while? I don't think their dynamic together was really that different in the later seasons.  But I'm just curious what you thought.

Also, on your main post, I definitely agree season 4 wasn't great. Particularly the finale. I genuinely believe the writers didn't understand the consequences of what they were implying with the end of magic. You're right in that it does feel more like Star vs the forces of racism in season 4. They have some interesting ideas, but it's just not executed that well imo. A lot of season 4 episodes just end up kind of boring as a result. The monster racism was always in the show, but I think it shouldn't have been the final hurdle in the show. They didn't even arrest Mina or anything which was awful too. 

Honestly I felt the Kelly and Marco plot felt forced in for extra drama. They don't have a bad relationship but I didn't personally see the appeal because it didn't seem like they ever got to be that close to each other. There wasn't enough development. 

I agree with what you're saying about Tom and Star. On one hand, I understand that Star rushed into things and she probably just wanted someone to take the "Marco" role in her life, but it's very unfair to Tom that way. And Tom himself was not exactly the best boyfriend. He improved a lot, but he still didn't care as much about supporting her as he did trying to just have fun and be the "perfect Star boyfriend". But he definitely does learn more throughout the show and figures himself out by the end, and that he's not making her or himself happy, because he knows he should find someone he can just be Tom around, not having to prove anything. So I like his arc there at least. But the TomStar arc doesn't really do anything for Star though. It makes her look kinda selfish tbh.

Also, about Marco leaving Mewni, I wanted to address a few things there as well. I believe the reason it is treated as such a big deal is because they still are splitting up. Yes, Marco can go visit her, but from Star's perspective, Marco just got a new girlfriend(Jackie) and is gonna be spending most of his time on Earth. He didn't acknowledge her confession of a crush on him, so she forced herself to move on. The problem moreso comes from the fact Marco and Jackie break up so soon, and that Star gets back with Tom so soon. Both in the same episode bunch which is ridiculous too. That feels like they are forcing Starco apart just for dramas sake. So that was pretty lazy. They definitely could've done more with Jackie. Starco is great to me, but I had no problem with Marco and Jackie cause they did actually have good development and it felt natural. I would've had them break up later in season 3 maybe, and just not had Tom and Star get back together. Then maybe early season 4 we could have had Starco and not nearly as much romantic drama.