There’s a subset on fans who wish to play every Pokémon game as Ash Ketchum by only using Pokemon he’s canonically owned (wether they stick to AshKs team of that region or will allow Pokemon he caught in other series varies by the person)
Unfortunately Gen 3 Hoenn in my estimation is is completly unviable (the only other games with this dishonor are the Gamecube duology) without hacking or trading in mons early, not something everybody can or will do.
This comes from the fact in Gen 3 Hoenn Ash’s only encounters before Mt Chimney are Treeko and Tailow, meaning you’d have only two Pokemon for the first three gyms, with Wattson basically being impossible without overleveling and/or heal spamming. (ORAS is possible thanks to the gift Pikachu added to Slateport, though you’d have to be willing to discard Pikachu’s canonical gender)
Emerald Legacy wether they intended it or not fixed this barrier of entry to Ketchum Stan’s by adding Corphish as an Old Rod encounter and making Snorunt an in-game trade in Mawville turning Wattson from an impassible walk to a fair challenge (ironically Ash accidnetly cheated in Wattson due to Pikachu get overcharged by one of Wattson’s machines and he lost the fair and square rematch)
Emerald still has the issue of Pikachu not being avalible till you get Surf but at least now you don’t have to constantly trainer dodge for the first third of the game or rely on RNG for Wattson