I guess you could go either way with their earlier stuff. Too Fast and Shout are heavier than the later stuff, but I'd still say it's hard rock when you compare to other stuff that was around at the time (i.e., Judas Priest, Sabbath, Iron Maiden, Metaallica, etc.). Still, I can see what you're saying.
It's when murder is justice that martyrs are made.
The stars are going out and the stripes are getting bent.