Like he only used most of his Sinnoh team against Paul. He used most of his other pokemon in all the other matches. We're in a 25th anniversary season, it's not that surprising people want to see some old pokemon. Especially since the writers themselves already spotlighted Infernape and Greninja, and keep showing his Alola pokemon and some of the Oak ones. Now obviously they all can't get used, but a few can.Ash has only ever used reserves in ONE league (Sinnoh), and none of them except Heracross and Sceptile actually accomplished anything of note. The rest were just jobbers. Battle Frontier is an outlier because it was a filler arc.