I mean metal has gitars in it and rock also has gitars in it so are they pretty much the same? I havent listened to metal tho so i don't know much about the sound of it but i listened to that nurvana song on the radio and that sounded like rock. Maybe that was metal? You decide.
Metal's existence is built on Rock. Metal is a more strong, Vibrant and shocking take on rock, It's meant to wow the audience and shock them with loud vocals and instruments. It's HARDER than Rock. The sound is more gritty and exciting, Unlike anything anyone has ever heard before. It's harder than Rock, Because it's Metal.
Musically, I would say yes. I’d say that there is a much bigger difference between AC/DC, Sex Pistols, And Pink Floyd than there is between Guns n Roses and Iron Maiden if we’re talking about music. Sure the whole “blues” thing and the several subgenres did kind of make metal its own culture compared to other kinds of rock music, But that does not mean that metal has been completely independent. Besides, A couple of heavy metal bands still use blues scales (Black Sabbath, Judas Priest, Pantera, Etc. ).
While I do agree that metal is its own culture, But punk, Emo, Goth, And progressive also had their own cultures compared to what we consider typical rock n roll. Besides, What serves as the guideline for rock music? Elvis? Aerosmith? Nirvana? These bands have not much in common.
So yeah, Metal is still a subgenre of rock music. Without rock, Metal would have never existed, And without metal, Rock would still be a thing. Obviously it would be weird to label Cannibal Corpse as just “rock, ” but like it or not, They are still an undoubtedly subgenre of rock music.