When the Emperor told Luke “Strike me down with all of your hatred and your journey towards the dark side will be complete!” He wanted Luke to try and murder him. Of course even if Vader hadn’t blocked the strike, Palpatine ran zero risk of being injured. Luke was the equivalent of a pesky fly. A Jedi uses the force for defense only. Vader was protecting the Emperor, no need to retcon ROTJ with this spirit transfer mediocrity. For TROS there is no way around the spirit transfer ritual. It’s an integral part of the plot, so discussion of its removal is moot.