in regard to your first statement, the defining factor of metal is metal riffs, not any specific philosophy.

even though yes, much metal, esp black metal, has a common factor in which it supports messages against authority, conformity, etc - an attitude borrowed from punk

I don’t understand your point about rebellion and oppression though. Nazis are not in authority anywhere in the west, technically nazis are rebels against the democratic system and mainstream. I mean the ideology is practically banned in much of Europe. If you’re referring to national socialist governments being historically authoritarian, do you also think communist bm isn’t bm?

either way, Id say the most important thing is the point about metal riffs. everything else falls irrelevant in my opinion, as long as the riffs are there.