A region typically seems to have an elite 4 and champion and that has its own professor and villain group. Johto has night and day while Kanto does not, so they're probably on different planets, where Kanto is tidal locked with a magical cave teleporting you between the two planets. They do seem to share the same villain group though, so maybe that makes them kinda like the EU?

If Alola is Hawai'i, does that mean Alola was colonized by Galar and Unova? Did Unova nuke Kanto and Johto? Was that the war that Lt. Surge was in?

Unova is just the NYC metro area turned into a region (so less urbanized and bigger). Anyway, Pokémon doesn't really have much worldbuilding. You're not supposed to think about this (but you can if you want to critique obviously).

Kalos matches pretty cleanly with the terre d'oïl whereas some future southern France region would be Occitania (in much older time European regions were named after how they said yes for whatever reason, Occitania says Oc and northern french France said Oui).

If it's anything like real life, what makes a region is some squishy stuff between linguistics, geography, modern cultural rewriting, historical conquests and oppression etc.

The Pokémon world went through some horrific war, partially this is a fan theory but people like Lt Surge ARE veterans of some war that used pokemon. Unova has, like, what is obviously a radioactive wasteland. Could be like Star Trek where nation states just stopped mattering as much after some enormous social upheaval and revolution following such a global conflict (perhaps Poké Stalin didn't stop at Berlin and backed the Greek commies). Perhaps to the poké citizens, some still hold onto the old lies like Nation State citizenship but most think of themselves in terms of occupants of a particular bio-region (as if Cascadia ever became an irl thing with hegemonic power, and whatever other bioregions) and borders don't really exist