The transforming Emperor quote seems to be from before Yoda was created, and the idea was that there would be a battle between Palpatine and Obi-Wan in which it would be revealed that they can switch between physical and ghost forms at will. This is seen in the first screenplay draft of ROTJ and I suspect that introducing Palpatine as a hologram was supposed to make him seem “ghostly”. That quote may or may not have been from before Lucas decided to end the Luke-Vader-Palpatine Saga with the third (in release order) film.