This all reads to me like the author had this big long term plan for how these two gradually get together, and in the end they didn't get to make it so they gave us the cliff's notes so that we know what the plan was.
Right, but how long was that Platonic ideal series going to be? As it is we got 38 chapters and a dozen bonus entries, so it’s not like the author was denied the opportunity to tell their story.
If a Uta-Kaoru yuri couple was going to be the endgame, the story had three hurdles to negotiate in regard to Kaoru’s character:
The story spent forever and a day having Uta accept that her love was probably hopeless and in Kaoru deciding that her marriage was unsatisfactory (something readers perceived in the first few pages of Chapter 1).
The story likewise spent zero time on Kaoru considering her sexual orientation, and (arguably) just slightly more in recalibrating her attitude toward Uta. (We got exponentially more explicit development of Uta’s wacky friends than we did about the nature of Kaoru’s feelings toward Uta,)
I also think it’s slightly bizarre that Risako now lives in the building next door (remember, Reiichi seems to live in the same building as his sister and ex-wife).
I suppose the big kiss is such a relief for the shippers assembled that we haven’t had any complaints that the longed-for yuri ending is only achieved by the MCs getting shitfaced drunk.