The issue with Snoke is that the way he was handled, especially in TLJ, doesn't just make him an "uninteresting villain", it makes him pretty much a complete non-character. He was not even a plot-device. He was utterly and completely superfluous.

He served absolutely no purpose whatsoever. He could be written out, some scenes altered and everything would be exactly the same. Episode 7 could've just started with Kylo as Supreme Leader and everything would be exactly the same.

Now, this wouldn't work with The Senate/Darth Vader, because The Senate has to be killed by Darth Vader. Palpatine's death was meaningful, because it was the point where Vader returned to the light side. You couldn't just replace Palpatine with Vader as the Emperor, because then he'd nothing to kill.

Snoke's death, however, didn't accomplish anything like that. The before-and-after of his death are the exact same situation. Kylo evil, Rey good. Nothing changed. At all.

(Which can be applied to the entirety of Episode 8 btw, the entire situation of everything is exactly the same as at the end of Episode 7 - literally nothing happened in Episode 8 that actually mattered. The most meaningful event was Poe losing his dope looking X Wing.)