You seem to have some prejudices. What's wrong with pimps?
harmony and discord are fascinating. The Devil's chords aren't at all discordant to us now, but back in the day? Welcome to the Jungle set my teeth on edge when I was 14, but now? It doesn't even seem that fast past to me.
With that preface, discord is the hallmark of metal.
As for the exceptions to the rules? Well, every artist/band slips genres once and a while. You describe a band/artist's genre by the majority of the music in their repertoire/opus, not by the rare odd ones out.
Heck, if we did that, I'd say that from Winds of Change, Scorpions was a pop group and not rock at all
As for Metallica, even 25 years after listening to them the first time, I think there's only one song of theirs that doesn't make me want to plug my ears. Maybe that's how I judge metal... by how uncomfortable it makes me.
Oh, and Devs! Please fix the Durability/Materials discrepancy!!!!!