Luke became so powerful in the novels that they had to nerf him to some degree just to keep the plot interesting.
To the point of absurdness. All those novels and comics and other stuff are often just a load of horse ****, invented out of thin air by some idiots for small children. They are more like magic stories, completely out of line with what we see in the movies. So I just disregard these creations, which describe Sidious as being able to mind wipe billions of people or destroying stars (and what the hell was he doing in the movies if he had such tremendous powers) and I can't even imagine what they wrote about Luke, who was so much more powerful so they even "had to nerf him". I'm certain he could accidentally destroy a star system by sneezing. What a load of crap.