i agree that lots of music is ridiculous and backwards, extremely rigid and codified, hardly evolving at all. have you heard any blues lately? :)

but seriously, the impression you describe is of your own making. metal is much wider musically and lyrically than the narrow subsection you used to listen to as a kid.

try UneXpect: https://www.youtube.com/watch?v=vVwl3kZwRX0