Hm I don't know. from the 'avant garde' black metal stuff, only Arcturus are mostly 70's hard rock and progressive rock. A lot of the others are just odd mixings of other genres like industrial, jazz, ambient and electronica. Fleurety on 'Department' play zero rock and roll. Ved Buens Ende, a band that has very little to do with rock also is considered 'avant garde'.
I think you're just making shit up so you can hate it uniformly. I do realize there's a lot of former black metal bands like Manes making switches into decidedly non-black metal territories, but you're putting an ideological spin on it by saying these territories are 'rock and roll' (which we hate 'cause it came from the darkie jews, right?) when it's just as well any other genre of music there is, really.