Palpatine ruled something like 23 years as Emperor of Galactic Empire. He has claimed he wants to "harness the full powers of the dark side". But did he actually learn anything useful that he didn't know as a Chancellor?

I'm mostly interested in Canon, I know that in Legends he could be reborn and create Force storms. But in Canon, his powers are mostly stagnant except the little adventure with the Lothal Temple and time travel. Am I missing something?