I agree with you on their relationship, we don’t get to see enough of the character interactions without something else hounding them, especially after attaining peace.
My wording was poor, by “sufficient ending” I was referring to how by the end of the story I felt the author managed to tick the minimum boxes and have some fun as well, for example, all the relevant characters managed to get some back story/thoughts told, we get to understand the antagonist more, the powers were explained, they get to do some sentai stuff at the end, etc. This one in comparison is abrupt.