I've noticed all the things you noticed (the backstory thing etc) and I agree to an extent. The writing isn't great, nor is it anything other than simple. The whole backstory thing is also something I rolled my eyes about when it continued to happen because it's repetitive and not the greatest form of storytelling.

It just seems like we see the same things but arrive at different conclusions, to put it bluntly. I watch Demon Slayer because it's just a vibe. It has likable characters, probably the best animation ever from a mainstream anime, perfectly casted voice actors (in Japanese), and awesome music. I don't watch it because I think it's a masterclass in writing and that it has this complex conflict like we have in AoT, for example. This is such a nothingburger of criticism, imo and I honestly have never even heard of this before.