Pokemon Moon has too many trainers with one Pokemon or not enough, too many Alolan Pokemon with very low encounter rates, Kanto Pokemon are the only Pokemon with Alolan forms, frame rate issues, too much handholding, too many cutscenes, SOS battles are bad, and etc.
Yellow is easy because you get all 3 starters, Nidoran and its evolution line are overpowered as well as Kadabra/Alakazam, Clefairy, and possibly some others. The game has broken mechanics that also make it very easy.
You think Yellow was challenging? I think R/B/Y are easy and broken games. I got Sun and Moon for Christmas and some other games. I don't like Sun/Moon much either but for different reasons. What did you get? I don't think you told me. Also, which starter did you choose? I don't think I ever asked you. I chose Popplio.