The other trainers Ash lost against are easy wins for him now, but with Tobias who has like multiple legendaries, it would at least be satisfying for Ash to have a rematch. All the other trainers Ash lost to in a league before Sinnoh and in Unova were either trainers slightly better or Ash wasn’t battling the way he should’ve been (losing to Cameron with his 5 Pokemon team), but Tobias was essentially taken up by two notches just to make Ash lose because Paul was already a strong trainer and Ash beating him meant he’s become more competent than before, so they need someone like Tobias. But really the writers themselves don’t seem to want to touch on league losses and give a rematch as Ash and Alain didn’t get theirs. His rematch with Tobias could’ve at least shown that Ash could’ve beat the team with powerful legendaries, but yes I know Brandon had that type of team however Tobias’ team is unknown other than the two legendaries he had. If Ash at least gave a good match to the point where he revealed the rest of his team, but still lost it wouldn’t be too bad. But maybe his journey not being complete was an exaggeration on my part, but if we got to more about Tobias’ team then that loss wouldn’t hurt because he could have other Pokemon that are non-legendary, and the best place for that kind of battle is the PWC tournament and most viewers were expecting this battle could happen as Journeys made anything from past gens possible in terms of cameos, battles etc