>>46121683Blue - Starters aren't native to Gen 1's Kanto
Lance - Charmander is certainly not native to Gen 2's Johto, though you technically fight him in Kanto, but Charmander is still not native to Gen 2's Kanto.
Steven - Some are rare, but all are obtainable in Hoenn.
Wallace - Again some are rare, but all are obtainable in Hoenn.
Blue (FR/LG) - Same as Gen 1 Blue
Cynthia - I'm gonna argue that Lucario is not normally obtainable in Sinnoh since you only get 1 Riolu Egg. So she breaks the rules.
Lance (HG/SS) - Same as Gen 2 Lance.
Alder - I'm not sure what the lore of Volcarona being in Relic Castle is, so I'm firmly undecided on this one.
Iris - All pokemon are obtainable in Unova
Diantha - All pokemon are obtainable in Kalos
Steven (ORAS) - Same as Gen 3 Steven
Gen 7 doesn't have a champion, but I'm gonna treat Kukui/Hau as the champion fights.
Kukui/Hau - Starters are not native to Alola
Trace - Uses pokemon that are native to this game's Kanto.
Leon - Starters are not native to Galar
TL;DR: Steven, Wallace, Iris, Diantha, and Trace are the only champions that use pokemon that are native to their own region.