It's not like the story just falls apart, the themes and character development are still clear and an obvious progression from what came before. In fact I'd say it's even more disappointing because it feels like all the elements are there, they just failed to bring them together in a satisfying way and instead settled for a really bland and cookie-cutter ending. Goes doubly so for Kano and Mahiru because the writing did more than enough legwork to give them a romantic conclusion but they don't bring it over the finish line for no adequate reason.