I disagree with everything you've said and implied and also I think you've entirely missed the point, when it comes to rating subgenres on a metal purity basis. All you're doing is making an argument for popularity disparity among the subgenres.
Not to mention Metallica aren't even that far removed from traditional heavy metal. Live in the future all you like, doesn't make your views more relevant than anybody else's of course, the fundamental objective point is that there is such a thing as metal purity and it has nothing to do with outsider reactions, popular opinion or a general distaste for foundational metal music.