Yes, Stover used early drafts of the film, and unpacked more ideas that ended up on the cutting room floor. I think it is a good illustration and one of the best Star Wars novels, bar none.
Palpatine has nothing to fear from Luke. Luke is not so strong that he isn't subject to manipulation, which is what the Dark Side does best. It takes even the best of intentions and twists them to selfish goals. The power of suggestions will work better if Luke is in the right frame of mind, and his mindset is already being twisted by the dark.
Thank you. That clarifies it better than I could.