It definitely is an art - everyone thinks they're a competent rhythm player until the engineer/producer wants them to double/quad/etc track their riffs
Then everyone suddenly wants their record to sound like VH1 with the guitar in mono on one side of the spectrum and the bass on the other
I've been working on that specific skill for a long, long time though, because I feel like that natural chorusing effect (if you can get it synced up and tight enough) is a hallmark of all of the best metal tones of all time.
Everyone complains that there is something missing in their "black album"/hetfield rhythm tone and then single tracks the guitars, ha
Naw dawg, thats a simple fix, you just gotta git gud