The historic classification is irrelevant for this debate, because Ozz was asking someone to justify why Machine Head is metal without reference to historic classification/popular opinion. You posted a bunch of songs from other Deep Purple albums that didn't address the question, and then when pressed, you pointed to Highway Star and Smoke on the Water as being metal. I've already conceded Highway Star even though I think it's borderline, but nothing else you've said changes my mind. Smoke on the Water is an arena rock song no more metal than say Whole Lotta Love. Space Truckin' is basically a glam precursor.