Had they chosen a different type specialization, a different character preferably not linked to Wallace, and created a completely awesome eighth Gym Leader for Emerald, then I might have preferred Wallace as the champion for bringing forth this awesome hypothetical character.
What about Drew? or Harley? I know he is an Anime character and I know he is into contests he still would have made a good gym leader, His pokemon are balanced and apart from Butterfree all of his pokemon are from Hoenn (Which he could replace with Dustox/Beautifly). I understand they wanted to use a water type gym for the last gym in Emerald because of where the Gym is located and I agree that Wallace had the same type pokemon, However you don't really expect to have to face another water trainer so some people might of boxed there grass/electric pokemon before doing the E4 as they are not need anywhere else.