I disagree on some of your points, I felt VI was one of the first games to have a cohesive OST whereas VII's offered more variety but lacked cohesion. My issue with re-using melodies is not that IX reworked old tracks from earlier games (that was quite creative) as much as it was the issue of it having three strong melodies that were overused in different variations that they ultimately became the three melodies you remember whereas I felt VI and VII both had a larger variety of memorable melodies.
VIII for instance has a ton of tracks but unless it was your all time favorite, I'm pretty sure the most memorable tracks most people could pick out would be one of the game's variations on Eyes on Me or Liberali Fatali, similarly I feel that IX's most distinct tracks are one of the variations of The Place I'll Return to, Melodies of Life, or Rose of May. Only Steiner and Garnet got proper leitmotifs of their themes which is why they probably stand out the most but considering Garnet's theme is itself a rearrangement of Melodies of Life it falls back to everything sounding a bit similar. My issue with IX's OST is ultimately the same as my issue with Chrono Cross though IX is a bit better about this, which is that I don't find the themes are tied to the situation as well as I would have liked. I blame this on the soundtracks being large enough to let every scene have a unique theme whereas earlier games, with VII being the last to do this, often had to re-use themes and thus reinforce it, making them memorable. For instance Steiner has a pretty memorable theme cause most scenes focusing on him actually made use of it, whereas Zidane and Vivi's theme rarely played beyond a few times and characters like Eiko, Freya, and Amarant got so few scenes to themselves that you often wonder if they had themes. Sometimes a track comes around that is kickass enough to be memorable and it works well for the scene like IX's Not Alone sequence, but I doubt you could name off the top of your head what track was playing when Atmos destroyed Lindblum unless this was just ultimately your all time favorite game ever. I listen to IX's OST and I often have to guess when a particular track played and while the music is very soothing and well done, I find it too easily falls into background noise with a few exceptions.
I like IX's soundtrack and it was in my mind the last really good OST by Uematsu as I feel X's OST is utterly forgettable beyond three tracks and XI's nice but again, forgettable.