Snoke wasn’t a Sith, and doesn’t call himself one. He’s never labelled, just as Palpatine was never labelled in the original trilogy. He’s more clearly established as powerful in the dark side, he was established to be in charge of a fascist movement. That’s all we really need to know.

It’s made clear that Snoke and the First Order came from the unknown regions, so that explains how our heroes didn’t know about him 30 years prior.

I agree they pulled this villain out of their ass, I just don’t feel they did anything differently compared to the original trilogy and they didn’t need to go into his backstory (especially with how unsatisfactorily they revealed him to be Palpatine’s modified clone puppet?)