I've been playing piano for over 40 years and other instruments almost as long. I'm a massive fan of classical music. If you think metal bands don't understand rhythm you obviously haven't listened to much.
I'm not claiming any band to be profound, but many have complex interplay between multiple rhythms, very non standard chord progressions, often non standard tunings, and even microtonal instrumentation.
You seem to be stuck in a world where everyone from Stockhausen suddenly stopped learning music theory. I'm telling you that you're wrong, and obviously not listening to enough modern music.
Stop being a music snob. You are free to like whatever you want but making glaringly incorrect statements about an entire time period encompassing many genres is going to get push back.