Yes, I agree with you this statement isn't the absolute truth. It represents the general direction of metal, it doesn't want to be exhaustive about all the metal world.
Personally, I'd never classify a genre being based on "general tendencies", which sounds like prejudices to me: anyway, as I said many times, I have to do this because this article has to be "encyclopedic". I'm a metallar, I know the world of heavy metal, and I agree with what you said.
I'll edit that section, then. Thank you for your suggestions and collaboration.