Wally's a strange rival, you only battle him two times in the entire game, he's technically the more "plot relevant" rival you take him to go catch his first pokemon he's the catching tutorial, he stops you from entering Watson's gym, and he's the last rival battle before the elite four he even gets all the rematches. Brendan/May show up more but most of their battles are optional. they didn't even fix it in the sequel they left wally as is and just gave him a mega stone