Who are the most powerful Sith/Darkside users in canon?

Two different continuities, and generalizing how people treat Luke”s opinion and projecting it to me is pretty goofy of you. 🙂

Snoke ragdolls Rey with ease and more fluidly than anyone else we've seen before. Vader has done worse against lesser opponents.

Yeah but Vader gets the “he wasn’t serious/was toying” excuse every time he doesn’t perform very well lol

Would Darth Caldoth or Darth Noctyss rank anywhere on the list?

Yeah likely