I've always felt regional forms was one of the smartest things the games ever did for Pokémon as a series and if the anime and card game had any sense, they would have seized and expounded upon that greatly. It reinforces the sometimes-forgotten idea of mons being real living creatures native to and influenced by particular environments, and they could differ in smaller ways than being a whole new mon with a similar design. Granbull in Johto might be Normal due to a long history of urban domestication, but a Granbull in Unova might be Fairy/Fighting due to the prevalence of Dark and Fighting types in the region. A Riolu from Sinnoh may have Inner Focus, but a Riolu from Alola may have a more carefree ability like Pickup or Own Tempo. There's a lot one could do with this idea by making small but interesting changes that would shift the mon's lore or how they battle, and Game Freak has really not utilized the idea to its full potential.