why could "Mettall ist schwer" not be "Metal is hard"? Duolingo insists on 'metal is heavy'.
Is there another word for hard that would be much better?
Is this term used to talk about both forms of metal (iron and music)?
No, most modern music genres are left with their english terms: Metal, Rock, all EDM genres
Some of them have a German term: Pop(musik), Volksmusik