I have tons of headcanons to differentiate the regions; hopefully someday they'll find their way into an actual story.
If you think about it, Sinnoh as a region seems to be a fairly mystical and eldritch place even by the standards of the Pokeverse as a whole. I can imagine how certain things that are taken for granted over there (such as Dawn Stones, for one; but also the ready supply of legendary dragons and fairies, etc.) would be considered faintly creepy elsewhere (this was, after all, the region that produced Cyrus and Cynthia, those Eldritch-Abomination-seekers). So I can imagine how a Hoennese trainer might look at a Sinnohvian trainer with a Gallade and say "EEW WHY DID YOU TRANSMOGRIFY YOUR PRECIOUS PRECIOUS KIRLIA YOU MONSTER!!!"
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If you think about it, Sinnoh as a region seems to be a fairly mystical and eldritch place even by the standards of the Pokeverse as a whole. I can imagine how certain things that are taken for granted over there (such as Dawn Stones, for one; but also the ready supply of legendary dragons and fairies, etc.) would be considered faintly creepy elsewhere (this was, after all, the region that produced Cyrus and Cynthia, those Eldritch-Abomination-seekers). So I can imagine how a Hoennese trainer might look at a Sinnohvian trainer with a Gallade and say "EEW WHY DID YOU TRANSMOGRIFY YOUR PRECIOUS PRECIOUS KIRLIA YOU MONSTER!!!"