It'd be an easy way yo shoehorn in more Pokemon fighters.
Not really easy... none of this makes any sense. You can't just have a different trainer as Pokémon Trainer's echo fighter, then have 3 different Pokémon. That's not only a different character, that is 3 different characters that have to be programmed in the game lol. No, if there's a Pokémon Trainer echo fighter, then all 3 Pokémon must be similar to Ivysaur, Charizard and Squirtle.