>>55581789Because even THAT bastard presumably got mogged by Cynthia, considering she was still Sinnoh's reigning champion four generations later.
Thus, Ash didn't need to rematch Tobias during the World Coronation Series, because beating Cynthia would by proxy "redeem" his battle against Tobias by following the logic of "because I defeated the person who defeated the other person that defeated me, I am stronger than the person that defeated me."
This is also why Ash and Alain never fought, instead he "redeemed" himself on that front by beating Leon.