I think I’ve heard the pitch that the Kreen Great One was (or that both were) perhaps Pyreen that took on appearances meant to blend the features of certain races (which ones? IDK) and only ended up looking like an avangion looks like.
I’m not sure i love this pitch, but there it is anyway. YMMV.
I also go with “all paths to Advanced Being are individual ones”… while dragons are all similar, there’s always differences, that get more pronounced as the dragon matures. While the standard avangion looks like a kleenex mated with a moth, that’s not the route that every preserver/psionicist will take.
In the Dark Sun group on Facebook (NOT the Sages of Dark Sun group), they have a listing of files attached to various posts (cleverly hidden in a button at the top of the page labeled Files).
One of the files, Epic Metamorphosis Codex, gives some fascinating requirements for the avangion metamorphosis spells (though I’m not one for all the True Name stuff).
Now if I could just figure out a way to actually DOWNLOAD it when my phone says it’s downloaded…
Edit: Can’t find a way to get a web address, so can’t post a link. If you find it, I’m talking about the Restorative Component of the epic metamorphosis spells, starting on page 36 (e.g., some defiler ash you took from an area before you restored it).