The characters stay in a holding pattern with each other for most of the book, but it comes off as repetitive and rather than giving tension.

This is interesting to me, because I also did not particularly like Book 4, but I'd put it down more to the combined set of tropes: not overly interested in May/December relationships, generally wearied by "let's practice-date, oh shit now there's feelings," rather than structural issues. This makes sense, though.