Palpatine (like Skywalker) isn't infallible. Especially in regards to combat, where he seems to emphasize a more scholarly approach to the Force and its aspects rather than overpowering his opponents; there's a reason that this guy surrounds himself with Emperor's Hands, Imperial Inquisitors, Imperial Stormtroopers, Sovereign Protectors, Royal Guardsmen, Shadow Guardsmen, Darth Vader: he doesn't give a shit about combat. Is he more powerful than any Sith? Yes. Does that mean that he can necessarily defeat them all in combat? No. Does his relative level of power suggest that he could, despite being a politician first and warrior a distant, distant second? Yeah.
Comparing the Ancient Sith to Palpatine is also absurd. They rely on Sith arcana and technology to enhance their level of powers. Palpatine's feats are extraordinary because they are of his own merit. Of all of them, only a case for Ragnos can be made to rival the Emperor in any arena.
Ragnos was clearly a skilled duelist, evidenced by the battles he won, the empire he held together, and the fact that he went unchallenged. Plus his gauntlets granted him increased melee skill.
He was also a master manipulator who schemed to have his rivals destroy one another. Don't be ridiculous and assume they feared him solely because he's "just that uber."
I don't know if he'd win or not, assuming this isn't DE Sidious. But I think its very possible that he could.
Palpatine is, technically, stronger in the dark side than Ragnos as of RotS. In terms of destructive output, Ragnos will never, ever compare. Combat, however, is a different story.