That’s just weird, as it’s always been super easy to pin a genre to Dimmu Borgir. Kinda surprised by this, but I’ve never had a foot in any dark alternative scene, so I don’t know how they see things.
Yeah, I know they both evolved into gothic metal/rock for most part, but it’s only a genre applied to the early, more black metal inspired stuff like Wolfheart and Irreligious, which both fits the black/doom/goth tag very well. Same goes for Tiamat. It were usually their earlier stuff that used to be called dark metal. Especially The Astral Sleep and Clouds. First one is very black metal oriented, albeit with loads of death-doom and hints of gothic. Clouds is more death-doom oriented with hints of goth, but the black metal is very much toned down.
But yeah, it’s a useless tag, although loads of great music has been categorized as such.
Nah, they’re pretty far away from Celtic Frost, but it’s hard to describe what they sound like. They’re incredibly unique, and even to this day their first few albums stands out as different. But old Bethlehem is what you’d get if you mix Katatonia’s Dance of December Souls, Celtic Frost’s Into the Pandemonium and Strid’s Strid and End of Life, and Deinonychus’s The Silence of December Deinonychus. Crazy good stuff too, if you ask me.