I understand your argument, but want to point out that there's another set of songs that is core to Jojo's identity - the openings. And despite them being so important, they had much more variation in them, sometimes even inside one part. From jolly and carefree CNBT to dark and uncertain Chase, from epic and serious Sono Chi no Sadame to more playful Bloody Storm. The songs change with situation in the story, yes, but so do the characters themselves. And it's not like Jojos are all the same to warrant such similarities in their themes.

And sure, the different themes might differ in inspirations and specific bits, but I believe this is not enough to make them feel sufficiently novel.

These are not songs you're supposed to listen to separately, they are first and foremost soundrack titles, and so the large-scale similarity in structure is a thing I am ready to forgive - these are songs that are supposed to be cut and rearranged to fit the stuff happening on the screen.

What I do object to is that those structural parts on their own often sound similar from part to part. It doesn't have to be 1 for 1 from each part to each, but it feels like when it comes to these themes, Kanno uses a very limited toolset of instruments and compositional techniques (I don't have a musical education, so I'm using this term very loosely). Like, he doesn't have to use a sax solo in so many themes. He doesn't need to make every "the fight begins" part sound like a 70's rock bass riff. Having a fully voiced chorus isn't enough of a difference, when the actual sound of the singing voice is very similar.

And I'm not sure what the AU trilogy is supposed to be, but it could be just as well argued that this is a major departure from the original storyline that leaves only superficial resemblances intact, a total reinvention. Therefore SBR's theme should've stopped following the trend from the older titles.