Honestly, I agree. The game is really short and really simple. The gameplay loop just isn't that rewarding for me, because I couldn't care less about scoring 100% on murder difficulty.
HiFi Rush is basically Guitar Hero with a different set of visuals. It was made for completionists who like to learn the ultimate moveset, because some people really enjoy that sort of game. I personally just consider it mediocre timewasting for a few hours on the level of a mobile game, except MUCH more expensive.