It doesn't bother me if a story ends short and was paced well. I'm just a bit tired of how Japanese romance stories always end after the confession and then just have a massive timeskip or no timeskip at all. There's been a small trend of that changing and mangaka showing relationships afterwards but sometimes it shows that mangaka don't know how to write that
I mean, that's a different narrative entirely then. I'm perfectly fine with this ending with them getting together because that's the story. To continue after that you have to find narrative tension from another source - which might work, might not, but it almost certainly won't be as good as the initial will-they/won't-they. It's the romcom condition as old as serialised romcoms have been around in any language - why Daphne and Niles getting together in Frasier is both the peak of the show and the start of its decline.
We want more, of course, because we want to bask in this lovely and beautiful relationship - but it's also flatter and less compelling than the travel to get there (or worse, more contrived in an attempt to pull dramatic tension in from somewhere). You can play it a few ways - first kiss, first time having sex - but the central problem and risk within the story is never the same. Kaguya-sama handles this pretty well for a while but is also hard-carried by a side ship in its second half and then completely falls off into contrived bullshit. A more interesting example I think is Takagi-san, which carries on with a low-stakes spin-off post time jump - knowing there's no tension so just being pure slice of life.