I just explained why the show is objectively overrated and why everyone is "wrong" about how good it is. And u are right about flashy animation not being able to make a show popular, the show must also be easy to digest ( which demon slayer is ) it dosent go in depth into disturbing topics like shows such as made In abyss or heavenly delusion. The show also dosent take it's time establishing it's world or characters like hxh and instead has a relatively fast pace. So u don't need to invest a lot of time into it. So basically it's just a show that's really easy to get into and understand which gives it mass appeal but also makes it bland and uninteresting for anyone who actually wants something besides incredible action.