>>27788321Sinnoh and Hoehn are too close to the mainland for meaningful change to develop. Pokemon best suited for each area can simply migrate.
Kanto is a very toxic and industrial society, so you only find Pokemon that can thrive there, but you head across the mountains and you find Kanto pokemon and now Johto ones, assuming Johto ones couldn't survive Kanto's enviroment.
The same can be said for Sinnoh. If a pokemon can't make it in Sinnoh, it would migrate to one of the other regions.
With Aloha it's either adapt or you're extinct.
