CiG
Harbinger of Metal
Definitely ain't the best song on there drongo, but also I suspect after a re-listen every song will get a 0.5 rating bump. I've only heard it in full once.
I think it's way too unique from what Venom were doing to be considered unoriginal. Even with lots of speed metal riffs, it's very much the first album I can think of to have that Scandinavian black metal sound, very different than anything that came before it. It does have a lot in common with Venom, even though Quorthon denied being influenced by them iirc.It's a fantastic Venom album.
You're just being fooled by the (amazing) production on the '84 re-recorded version.
The parts that don't sound like Venom sound like Venom's main influence Motörhead. Jonas Åkerlund himself stated they were exclusively influenced by Venom in those days. There's nothing particularly unprecedented or "Scandinavian black metal sound" about that album to me.