I know there is no one good answer to satisfy anything, since we know Palps was literally put in the movie just for marketing reasons/nostalgia/just cuz/who cares why. I also understand doing the whole transfer thing is what Sith have been doing the WHOLE TIME gives us … somewhat an answer. And yea, you can go that route to help explain all this. Sure. And good points with it.
However I personally would not want to make that implication. If a person was to sit down and do a Star Wars Marathon (Hal’s for sure for the PT!) there is “movie logic” that Palps talks about Plaguis who was basically figuring out reversing death, aka UNLIMITED LIFE WITH UNLIMITED POWER! (hahah) … but at this point didn’t have the secret to unlocking that. We even have Palps talking about figuring it out. So, we have Palps, who as a Sith is all about power … of course he would want to live on forever, would continue that work. So it something “new” by that time. (Remember, by ROTS, there was no force ghosts [till the end of it for Jedi to train on that] or a way to stop death)
Fast forward to the last movie. We see that Palps was indeed working on that, and was somewhat successful. What was one of the ways? Well with changing the Snoke vat to Palpy vats, we see he involved cloning. (That change was such a simple and smart change editors did!) And the whole transferring could have been either him figuring out fully or partially from what Plaguis started.
Personally, I would be ok with keeping the line “The Dark Side is a Pathway…” since it would more so connect to the audience to ROTS … which hey! Palps talked about this topic! So it’s really a line to help the audience connect to that movie.
Again, it isn’t perfect, but having it more of Palpatine doing this and not just “Palpatine wasn’t a person, he was all the Sith in a body! The Sith are no an individual, but a bunch of guys and gals in a body impersonating a person!” kinda takes away from Palpatine. Another instance of “This isn’t the bad guy in the story, it’s this new guy that get’s introduced at the end.”
Again, I want to stress just my view and it isn’t perfect by a stretch since there is no perfect way with Palps, who was pretty much thrown in the last movie “for reasons.” I would like it if it was complimenting the movies/“movie logic” that came before it, not “rewrite” them.