They sound like as B.O.C. if you ignore all nuance, maybe.
But why would you do that?

Then there's the matter of Opeth's 3 last albums where they go full on 70's prog worship, but I was thinking of the older albums as being their defining sound.

You seriously don't hear it?

Not really.
Show me an Oyster Cult song that proves that we're not just talking moderate similarities here and there.

I like how it never sounds anything like Opeth except there's guitars.

Fosho

Eh, BOC weren't that good when they were playing prog stuff anyway. Their best stuff is where they just go all out and kick your ass with 70's heavy metal:


Pretty much agree with this, especially just going off of late 80's and 90's examples of the genre.

BÖC aren't metal tho

Metal doesn't even exist, it's all blues.

No, but they had some metal songs imo.