First off, I absolutely would NOT be hard pressed to find a manga with more romantic misunderstandings. That's not to say TC isn't guilty of dragging things out, just that plenty of romcoms are WAY worse.
And out of the entire cast there are definitely plenty of couples that do consistently develop and explore later stages of their relationships. The ones that start out or become formulaic definitely stick out the longer you read, but just saying the romance element is "thin" I think isn't giving it enough credit. That's highly subjective to begin with, and sure there's plenty of "I just like you" or "he's so nice" - but I think despite that there's still a pretty decent presentation of relatable elements and dynamics in relationships across a broad cast, and even some of the more boring couples would have a few standout moments.
However, yes, there is a point where things start to drag out. I honestly think it's fine to skim through certain parts because of this, since there always going to be some couples you're still interested in seeing even if a few are dragging things down. And it does end well.
And the good thing is the format/tone of this manga makes that pretty easy to compartmentalize things. I don't know WHO made an excuse that it was realistic, but I'd argue the opposite. There are relatable elements, but the actual events occuring are usually explicitly caricaturized. You get a sense for this in the very first chapter, but by the time people are hugging afterimages and communicating in morse code I think that premise is pretty clear. Really I'll tolerate a million failed confessions if it's engaging each time.
The problem is more that the author attempts to have certain storylines span the whole series while at the same time trying to have individual ones be relatively self contained, starting new ones, having them crossover with each other. If you're trying to tie this many stories together without planning it all out ahead of time the pacing of some of them is going to suffer. And it does.
I think if I reviewed it right after a straight read through I'd remember the parts that were annoying more strongly and agree more with your perspective - that it was just a weak formula from the beginning and that I would have tolerated more if it was shorter. But upon rereading there's a lot of genuinely refreshing, original, and endearing stuff from the very beginning, and I'd say that quality never totally goes away, it just gets bogged down over its run the way serializations often do.
Ultimately though all this does amount to me agreeing that it should have ended sooner. I actually don't disagree with most your assessment aside from some minor phrasing caveats. The only reason I felt compelled to @ you at all was the "hard pressed" bit. I genuinely think that's an absurd claim.