Well, with SWC now over, I can take a further look at this TBH.
The problem with that? I have a lot of siblings and my home is a one-Switch household. Ergo, not a lot of play time
Unironically suggesting that you look for an abbreviated Let's Play, since the Pokémon games tend to not be plot-heavy anyway, you can breeze through a complete LP without missing anything so long as they take stuff like optional quests, and don't skip cutscenes or something equivalent.
So, the first major thing that comes to mind culture-wise with Kanto: people come of age early there, and it has Rota, and ninjas
Might be my impression from the dubs I recall (mostly Spanish) but my understanding is that Rota is a neighbouring nation and not part of Kanto, as it is described as a Kingdom (which also doesn't map with how geopolitical organization of Japan looks like if the anime follows IRL Japan conventions for Kanto/Johto/Hoenn/Sinnoh). That said, even if that was the case they're nearby enough to share cultural influence with one another.
...I just realized that I'm going to want something else, before I culture build. History. And it's been ages since I've seen the movies/episodes where they mentioned how long ago things were... I know about PokeAtlantis, Pokemonopolis, Damos, etcetera, but I don't remember the numbers. Great. Any help?
Bulbapedia has a page
detailing an official timeline of the animeverse though I am not sure if it considers the movies or not. The situation of the movies is a bit hazy in that at least some of them are or should be canon.
Some quickie pointers I can recall that could be relevant for your concerns about Champions and high-performance Trainers general:
* Damos was M12 (Arceus movie) and that is stated to be around 800 years before the events of the anime. It is to be said that [i}unlike[/i] Rota, Michima (where the movie takes place) is not said to be a separate geopolitical entity, and is perhaps something equivalent to a district or commune within then-Sinnoh (which, if going by PLA timeline, should also have been then-Hisui).
* In the anime the position of "Trainer" might be relatively recent. It's at least 40 years old (M4 / Celebi movie) and almost definitively not older than about 300 years which is when the known Leagues started (OI is said to be ~300 yr old and I think Evergrande is said in the anime to be about 200 yr old?).
* The anime is quite fuzzy with historical details for stuff like Pokémonopolis or the confrontations if Kyogre and Groudon across history. You are allowed (heck, almost required!) lots of leway if you are going to do Alternate History worldbuilding.