Did you really? It's just so hard for me to believe, I've been playing since Pokémon Blue, I played every single game except Let's Go, and Ultra Sun was the hardest game of the series hands down, to the point I didn't just have trouble with every totem battle but also with freaking normal trainers with a few Pokémon in their teams. That game made me get angry at how many times I kept losing battles.
Comparatively I find gen 1 and gen 2 to be the absolute easiest games in the series with only gen 6 being the exception.
Ha! Really? As I said on another post, for me Ultra Sun was really easy. It took me a while to complete it, but because since I got a job I just can't find enough time to play, however, I didn't have much trouble throughout the game. If you stick to a team they level up like crazy. I don't even remember which were my six Pokés, because most of the battles I beat them with just Decidueye and Malamar. And I'm not even of that kind of player that breed the best stats or soft reset, I literally stay with the first Pokémon of each species I stumble upon.
In the other hand, I bought the Virtual Console version of Pokémon Yellow, and I barely made it to the 8th gym, and I think to this day I didn't even make it to the League, but mostly because I transfer most of my creatures to the PokéBank xD It was just so hard to level up my Pokémon. Pikachu, Butterfree and Nidorina were my strongest Pokémon, but it felt just really complicated to advance through the game. There were even times I didn't even know where to go, 'cause I already forgot the storyline.
Btw, I need to start playing UltraSun again to complete the Pokédex and bring all the Pokémon from my previous games to have them ready for whatever thing they announce to transfer them to Gen VIII.