Varathron is somewhat disconnected from both BM lineages on this album. You can't really say it evolved from the Venom>Sodom>Sarcofago>Blasphemy>Beherit line anymore than you can say it evolved from the Venom>Sodom>Sarcofago>Mayhem>Burzum line. This is further evidence that this album at it's core isn't black metal. It's a black metal mimic. It's heritage is death metal and doom metal. There is much, much more Candlemass working in Varathron than any other influences. But I think the argument that Varathron is black metal is the classic "sum of all parts". With Black Metal art, the intent is as important as how you arrived there. The nuts and bolts of Varathron may not have been black metal, but it's intention was in the spirit of black metal.
Still, for me, the album invokes just a different spirit than other black metal of the period. When I am in the mood for this album, I'm not necessarily in a black metal mood at all. It doesn't have the desperate fanaticism or feral hatred that is often found in black metal of this era.
It's truly a special album. One of those albums that nearly stumbled into it's own genre.