Good Harems don't exist, huh. Interesting take there.
I don't read much here, I'm an author only, but I've read or watched enough anime/manga to know, that there are actual good harem stories.
One of my absolute favorite stories ever, is Highschool DxD. Romance makes sense, even the reason Issei (MC) is stupid to recognise that these women like him has a (more or less) logical reasoning behind it.
He starts out as a perverted nobody, so yeah, the entire boob thing is just fanservice, and without it the story would be just as amazing (minus for some of my favorite plot points), but that's not the same with the harem reasons.
#SPOILER INCOMING
Here's a generic breakdown for why it makes sense:
Rias - Issei was the first person to look at her as a girl, rather than the sister to literally Satan.
Akeno - Issei was the first person (after her parents, plot goes into it, I don't wanna spoil much), to accept her as a half-breed, which has made her super-concious about it, throughout her life.
Asia - he literally saves her life.
Xenovia - she's sort of the weird one here, but even her part is relatively reasonable. He saved Asia's life, which was kind of a big thing for her, as well as he's more or less just a test subject for her, to 'mate'.
Koneko - Once again, the whole acceptance theme of literally the entire story.
Ravel - again, sort of a weird one, and I can't really reason, as I didn't read the entire light novel yet, but again, he managed to pull her brother out of a really shitty place, so I guess it kinda counts.
#END OF SPOILERS
But then again, Issei sort of chose one for himself, and he looks at the rest of them as really great friends. He literally wants to be the Harem King (mind you, more than likely a reference to One Piece), and he does that, but he doesn't use them.
In my opinion, Highschool DxD should be the format harem stories should take.