When we were kids, that was your beloved AC/DC, my beloved Purple, and bands of that ilk, Zep, Sabs so on. Now Metal is bands with screaming /cookie monster vocals and hitting their instruments so hard it's amazing there's anything left. So the definition has shifted, and that may need to be further defined.
I agree that rock has changed alot especially Metal. 70's metal is so different from 90s metal.
Music changes and evolve and as a result we have a wide range of rock music sub genres.
70's Paul McCartney's Wings music, 80's Hall & Oates music and 90's Gin Blossoms music are all rock music.
Rock music falls under a huge umbrella, from Death Metal to Alternative Rock to Pop Rock. That is why i Love Rock. It is so diverse and awesome.