The main problem here is not the manga's structure, but people not getting said structure. If you go in with the assumption it will follow the "main pair" as the central driving plot you just misunderstand the point. Shiramine and Kurosawa are the framing device that holds the narrative together, but ultimately it is a story that follows relationships at the academy.
I remember starting this series and just getting confused a lot. The first couple of chapters made it look like a fast-burning short-ish story (remember, Kurosawa’s already out there on the balcony biting Shiramine in chapter 2), then suddenly we switch gears to Moe and Mizuki, with the first two characters in the background—I thought I must have missed some chapters or something. (The surface resemblance to Comprehensive Tovarisch, which was already well underway if I recall correctly, didn’t help me keep things straight in my head either.)
But by the end of the first volume it was clear how the structure was going to work (and the Little Theatre made it very obvious that if you didn’t like lots of characters, this probably wasn’t the place for you). For quite some time, whenever a new chapter came out I kind of yearned for the OTP, and I never could quite decide if the “other” chapters were better or worse with no OTP at all—the little Yurine/Shiramine cameos and “guest appearances” just reminded me that the parts I was reading weren’t my absolute favorites.
On longer acquaintance, though, I really came to like the structure a lot. It built a dense and plausible (given its explicit and implicit premises) world around the OTP, and the diverse romantic struggles of everybody made the basic Kurosawa-Shiramine conflict seem like less of a game with only a few possible moves and more like characters actually growing up and growing together over an extended (or so it seemed in narrative terms) period of time.
I’m not really familiar with many stories (romantic comedies, in any case) that have a structure just like this one—you’ve got stories with an A, B and maybe a C plot, or you’ve got long-runners with fairly open-ended ensemble stories, but I myself haven’t run across anything quite like a story with a central pairing surrounded by a whole constellation of subsidiary pairings that take center stage for long stretches.
This one had its own rhythm, and I understand why it wouldn’t be everyone’s cup of tea. But I definitely think it accomplished what it set out to do very skillfully, and (for me) very enjoyably.