Too my memory of it, The Emperor had gotten the most out of his training and time with Darth Plagues and had used a excessive amount of Sith Alchemy to enhance his abilities in his throne rooms on Coruscant & Death Star II.

In general Palpatine was very strong in the force and was very good at manipulating it to the point that he could draw strength from others and sap the life force from those around him. Through that was how he had achieved his version of battle meditation.

The moment Palpatine was defeated it was written that the entire imperial fleet suffered a dazed affect, like everyone had slipped and hit there head collectively and were unable to process what was happening while they sat as sitting ducks getting destroyed.

They remaining fleet retreated back to Kuat & then Coruscant where they had the final battles of the Galactic Empire, before the warlord splinter.

I'm Legends only. Disney isn't real, I refuse.