I'm sorry, but saying it's the novelization of the movie does NOT equate to it being widely read.
As you've acknowledged, it was cut from the final film (if it was ever in the script at all), so IMO it's irrelevant and not canon. It's like those early ROTJ drafts where GL was going to have Yoda or Ben's force ghost block Palpatine's lightning to save Luke. If this is canon, then it's hypocritical to say a force ghost can't physically interact with/affect the living world. We don't get to pick and choose which discarded drafts are canon and which are not.
No its not like early drafts thats not how movie novelizations work but if you need to tell yourself this to enjoy tros more power too you. They were very vague with the emperor for a reason cause the whole thing is a confusing mess. The novelization is as much canon as the movie again if you read it you would know this. Everything you see in the movie is in the book with word for word dialog so if its irrelevant so is everything you saw in tros with your eyes lol.
Thats like saying lord of the rings novel isnt canon cause peter jackson omitted a few characters from the movie lol. Movie doesnt override the book its based on. The rise of Skywalker book is the complete story the movie is based on but they couldnt fit everything in the book in the movie. Its the same exact story with more details, im sorry i dont get your arguement at all. If it was some random book or some pre rise book sure but its the actual movie novelization lol