... why would the Rotoms have Ghost moves and Shaymin not have Flying moves in regular STABmons? (I tested this for confirmation: STABmons will reject Land Forme Shaymin with Flying moves) It makes
more sense for Shaymin Land Forme to inherit Flying moves than for non-Ghost Rotoms to inherit Ghost moves, since Shaymin-Sky will revert to Land Forme if frozen in the middle of battle, whereas Rotom cannot change Forme in battle, period.
I've been assuming the Rotoms don't get Ghost moves because A: nobody ever runs Washtom or Heattom with a Ghost move Rotom doesn't normally get and B: Rotom alternate Formes getting Ghost moves would only make sense if all other Pokemon that change Form(e)s and types without losing Form(e)-specific moves had the same dynamic. (This only currently matters to Shaymin and Arceus, but you are banning Arceus from that dynamic
here and Shaymin being barred from Flying moves is just inconsistent and baseless -Arceus at least breaks the meta by being consistent with the rules)
As-is I'm baffled as to why Rotom, and Rotom alone, should benefit from such a favorable ruling in regular STABmons.
On-topic, I was focusing on Destiny Bond because it gives Rotom yet
another way to surprise-screw people. Of course, since apparently you can do that in STABmons...
So instead let me point out that now Meloetta-Aria gets Secret Sword and Vacuum Wave. That makes it that little bit more terrifying.