The original voice actor was awful and the hologram–setting aside it’s a hybrid of an old woman and a chimpanzee–looked absolutely nothing like the Emperor in ROTJ, even less like him than ROTS McDiarmid does.
I don’t know, while it’s true that Theatrical Empire Palpatine ‘‘sounds’’ nothing like Ian McDiarmid, the visuals… Well we barely even see what he looks like in the first place. His face is almost completely covered in shadows. I’ve seen the argument made that showing his face as clearly as the redone version does sort of takes away from the mystery of the character, and I don’t think the original shows him clearly enough that it ends up becoming particularly jarring in Jedi to begin with. Like, if they had kept the original hologram and merely redubbed it with McDiarmid’s voice, I think that would have worked fine.
That said, yeah, I prefer actually having the same actor in all the movies, even if the implementation of the change was… less than perfect. I guess Adywan’s version ends up being the best by default here.