>>48373612Game Freak call them eras, IIRC. Either way
>>48373616 has it right. Legends isn't set in a new region, given they called it Sinnoh of old in its reveal trailer, starters are all repeats in some fashion - from the wild future Sinnoh starters to Prof. Laverton's set of three and of course the whole hinting how the events in Legends eventually give rise to Sinnoh of BDSP.
Come back Pokémon day, they'll have what you're after then, a new region, with new starters, professor, champion, gym leaders, rival, new pokémon of all flavours, new evil team, new save the region/world plot, new meta.