In the broadest possible sense there are two "schools" of heavy metal pre-1980s (kind of like how there are two schools of jazz tenor playing, you're either a Hawkins disciple or a Lester Young disciple). Theres the European school: Black Sabbath, Deep Purple, Uriah Heep, Budgie, Rainbow, Judas Priest, etc. There's the US school: Van Halen, Aerosmith, Ted Nugent, Kiss, Alice Cooper, etc. In the 80s the stuff generally considered to be "heavy metal" was bands influenced by the European school and the slightly later NWOBHM offshoot. This extended into newer genres like thrash, doom, power metal (the 80s definition of the term, not the modern definition of the term), etc. Thrash then later begat further offshoots like death metal. The "hair metal" stuff was generally bands influenced by the US school...and mostly Van Halen to be honest. The US school to me has always been right on that cusp of hard rock/heavy metal, generally being more focused on upbeat party rock and stuff that "chicks dig". The influence of Led Zeppelin kind of falls somewhere in between the two schools as Plant's stage presence was a popular influential thing for hair metal vocalists to emulate...if you could mix Plant and Steven Tyler together you basically have every frontman for every commercial metal act during the entire decade. This is of course an over-simplification, but I think it works from a cursory standpoint. If you read interviews with Motley Crue or Ratt during the 80s they always listed bands like Kiss and Aerosmith as primary influences. If you read interviews with bands like Metallica or Slayer they usually mentioned Sabbath, Deep Purple and all the NWOBHM bands. Anybody who thinks hair metal bands didn't care about the music is just ignorant. They cared no more or less than musicians in any other rock genre. Not saying it was all gold, but the implication that because of their appearance they didn't care about the songs is just asinine. Any thought that musicians in thrash or speed metal or just rock bands didn't care about the way they looked is also completely misguided. FWIW, as someone who grew up as a metal kid in the 80s/early 90s the genres weren't nearly as defined as they are now. We'd listen to Metallica or Iron Maiden or Megadeth and then something on the poppier end of the scale - Crue, Warrant, Slaughter, Cinderella, whatever. Yeah some people weren't into the extremes on either end (Firehouse or King Diamond, for example), but for the most part metal was metal and it was all rock.