Oh man... I had that first Saint Vitus album. That one was really divisive amongst my friends... punk? metal? punketal? munk? Nobody could agree on what 'type' of music it was.... but we all agreed that the guitar sound was BRUTAL.
And I draw a strong line in my mind between the NWOBHM, and other metal from the same era.
It's like the NWOBHM forked and became Hair Metal (Poison), Van Halen-esque (Motley Crue, Sammy Hagar, Scorpions), Straight-up Metal (Metallica, Sepultura, Megadeth, Mastodon), and Black Metal (Mercyful Fate, etc).
And then a bunch of us metalheads in Seattle started mumbling, messing with song structures, and playing with really grungy distortion... and inadvertently invented Grunge. For me and my friends, we were just being a modern Black Sabbath, but in cut off army pants and flannel shirts.