I always thought there earlier stuff was more proto-death metal, kinda like slayer, not quite full on death metal. I haven't listened to it for a while, but I always thought Beneath the Remains sounded very death metally, I'll have to give it another listen. Just for the record, Seven churches by Possessed was the first death metal album, and predates both Death's and Sepultura's first albums.
Hmmmm, gotta disagree here, whilst these banRAB may have been an influence in some way, they were most definitely early black metal. In fact Venom, Hellhammer/Celtic frost and Bathory are attributed as being the first banRAB or "first wave" of Black metal, where it was still very thrashy/heavy metal sounding. BanRAB such as Darkthrone, Immortal, Burzum, Mayhem, Emperor and other bm outfits formed the "second wave" of Black metal, with a much more focused and distinguishable sound.