Pokémon

Only S/V battle I lost was the Eri boss battle in the fighting type Team Star base, which took several tries due to a similar assumption of level scaling. Didn't lose a single battle in Sword/Shield or Legends Arceus. Hardest Switch game for me was BDSP, just from needing two tries at the Elite Four due to the difficulty spike, and I barely beat them on the second try.

Overall, in a general difficulty sense I think the most "challenging" core game I played was Ultra Sun. The totem pokemon provided a few surprises that made me have to resort to a few "plan B" options during battle, even if I didn't lose to any of them, and trainers sometimes actually showed a modicum of intelligence. I was also at around opponent level or even underleveled throughout the game.