Ok so I had a pokemon worldbuilding thought for my oc stuff, but I'm gonna drop it here for anyone to consider bc tbqh I feel like it just makes sense:
What if, as legendary incidents see a sharp spike in occurrence, the title of "champion" becomes synonymous with being a sort of keeper or tender of Legendaries?
See, in a lot of games, npcs who speak of the local legendaries tend to talk of them more in the sense of folklore or cryptid or myth - creatures people haven't laid eyes on in ages, who aren't even positive existed. It's not until respective "evil teams" or whatever per each game plot actively stir up trouble and wake these mythological wonders up. And then in a lot of cases, they're Up for the foreseeable future.
Regions who only had champions for essentially sportsmanship purposes, now have to task their proven strongest trainer - who perhaps already faced and took down their local rampaging legendary, if you're following game structure - with the job of making sure the legendary is left unbothered and also not running rampant.
What does this mean? Well, it's different for every region, every legendary, and each champion is going to have a different approach on it. Some of them capture the Legendary and train it as their own, some of them keep it in boxes (pastures), some of them simply keep an eye on its home to make sure no one trespasses and stirs up a fuss. Some regions, like Alola and Johto, seem good about having protocols in place for how to interact with and respect the legendaries. Others, not so much, which means that while the title of Champion comes with this added task, the actual job descriptors get kind of vague after that.
I think too, this sort of added responsibility would explain any need for a champion changeover, too. A lot of champion npcs seem implied to have been the champs for a while - and, depending on how you interpret the game mechanics that allow you to re-challenge them, they often maintain their status even once you've defeated them. While it's simple to argue that it's not that common for trainers to reach the level of skill required to dethrone a champion, I do think it'd be interesting if the champions step down and trade off for someone who has already quelled the legendaries themselves, because the 'current' champions were not qualified to handle them.
Tl;dr - the games don't offer a lot of insight on what would happen with legendaries in-game if the player didn't choose to catch Every One and tame it, and the occupation of champion always seemed to me like it'd have a limited set of active responsibilities with a lot of gaps, so I decided to take care of two zapdos with one stone and brainstorm a solution for both! This isn't heavily canon-compliant, and isn't meant to be, but hopefully it feels plausible enough to work with!
Also - If enough people are interested, I may share my flexible breakdown of how arduous a task being a legends keeper is in each region! I cited Alola and Johto as being a bit easier with existing protocols built in, but I've put some thought into just how challenging each region could be to oversee, and how this could influence champion approach!
As mentioned, feel free to run off with this concept for your own ocs! And if you want, tag me in lore posts for it! This is my oc blog, but I also like to showcase other peoples' stuff, and I'd love to see how people approach this concept!