It’s true that the story of Demon Slayer is simple: Tanjiro Kamado is trying to save his sister, Nezuko, who became a demon, and in doing so, has to vanquish Muzan, the King of Demons, by mastering an ancient style of fighting that utilizes breathing techniques. Again, this is not the twisted, layered narrative of Attack on Titan, but it does lack the depth of, say, One Piece, which goes beyond “I’m the next Pirate King” to involve deep character conflict.
I don’t mean to imply that Demon Slayer is bad for being simple, as that’s done on purpose, but there’s a good reason, as this is an introductory Shonen anime. Not everything has to include the levels of narrative found in a Mobile Suit Gundam series; sometimes, it’s okay for a show to look good and be fun.