It’s a name that was created for that storyline. Palpatine, much like the term Sith, was used for the OT and its marketing materials. Sidious was treated as his truer name, with Palpatine being more of the disguise.
Every other film in the franchise, including first instalments of two other trilogies. This wasn’t like Lord of the Rings, where it’s one story spread over 6-9hrs. It was a first story, but he failed to tell a complete story.
Was the word “Sith” ever uttered in the original trilogy, though? (excluding early drafts, deleted scenes and the EU material). Can’t remember if it did.
I believe I’m falling in a middle ground between you guys. I definitely think TFA could have used a lot more originality but it’s a fine film, and I like Johnson’s themes and character arcs for TLJ even if their execution was hit-or-miss.
Anyway, Rise of Skywalker is a film that’s already packed with fan-service, and seeing as there’s not much we can do to turn it around and make it a more character-driven story, I’m open to embracing more fanservice elements (red lightning, green Sith magic, name-dropping Sidious, etc.).