My case for Deep Purple and GNR (at least Appetite)
IMO this is very much like the debate about movies like Se7en and Silence of the Lambs being horror or thrillers. A big elephant in the room when talking about 70s acts being metal or not is that Sabbath unleashed hell at the start of the decade. THAT 100% is metal, but I would say just like other stuff there is a scale. Personally, I bristle when people say Led Zeppelin is metal. To me that is the example of a hard rock band. To my ears there is a world of difference between their 1970 albums.
As far as Deep Purple, to me they also flipped a gear dipped into the metal category in the early 70s as well. There are songs and parts of songs on In Rock that wouldn't sound out of place on a Sabbath or Priest album, IMO. For example - Bloodsucker. My other thought is that if you replace Lord's organ with a guitar, there would be 0 argument. Does that mean we are saying metal can't have keyboards in it? No, they don't operate in that zone most of the time as Sabbath or Priest later, but to be there is enough there and they sound different enough from other hard rock bands that I give them the metal seal of approval.
When I was posting about GNR I was specifically listening to and thinking about Appetite. 10 of the 12 songs sound like it's the soundtrack to the night my buddy and I got way too drunk on swamp waters, puked green in the gutter on the corner by the dorms, proceeded to pass out on said corner for a couple hours, and woke up smelling like piss. It's angry, raw, dangerous, and sleazy. I think because of those songs I tip the album into the metal category, but I am less convinced here. If it's not metal, it is the Seven of albums in that maybe it's as hard as you can get without being metal? That's why Paradise City draws my hatred so much - because buried in this awesome album I just described is this dumb song with that chorus "where the grass is green and the girls are pretty". It's dull, repetitive, overly long, and reeks of record company interference (I have 0 idea if that is true, just roll with me). Sweet Child doesn't get the same ire because I think is still has a little more grit. I still love it, but it honestly does stick on that album in a similar way. Does anybody remember that original artwork with the album?
I am not overly familiar with Aerosmith, but I've never heard anything by them that gets to the same zone as Deep Purple or had the dangerous edge as early GNR. I think they are another prototypical hard rock band like Zeppelin. I would be open to arguments otherwise though.
Just one dope's opinion though.