I get that people would wanna use their favorite legendary, but to have a child capture and use a legendary pokémon just seems to... make-believe. I don't know if I'm alone here but I've never actually caught any legendary Pokémon, instead usually opting to run away from it. I've never even caught Suicune which is my favourite pokémon.
I find that I agree with this idea more, as most legendaries serve some sort of importance to the region they're from. For example, its hard to understand why the Lake Guardians are in Galar, when they should be guarding their respective lakes.
Well some ideas I had sort of explain this away:
- Dream Recreations: The Legendary aren't actually there but what you have is an "avatar" of the Legendary pulled from the Dream World; it doesn't actually exist in-canon. You get them by entering the dream of said Legendaries, asking & answering the question "what does a Legendary Pokemon dream of?".
- Synthetic Replica: Instead of catching the Legendary, you help a group of scientists study the Legendary and they create a replica of the Legendary. It acts like the Legendary and as powerful as a Legendary is in battle, but it's not actually alive and doesn't have a Legendary's godly powers.
- Illusion Form: Instead of catching the Legendary, you can choose one of your Pokemon to create an illusion around themselves which essentially transforms them into the Legendary.
- Realistic Hologram: The Legendary is a hologram but the Poke Ball it's kept in has been modified so that it makes it solid & capable of interacting with the world (thus compete in battles).
- Summons: We can go the Final Fantasy route and, instead of catching the Legendary, you just are able to summon them in that moment in time.