In other words, his return is meant to come out of nowhere in TRoS.
Nothing was meant to happen because they had no idea what they were doing. JJ himself admitted Palpatine was not the intended outcome of the Disney trilogy and they just kinda winged it.
I’m not knocking your opinion at all; if that’s what you personally want to take from it then more power to you, but you’re kind of framing your argument like it’s an actual fact when we’ve got the filmmakers themselves contradicting that.
Even then, his return was already set up in the opera scene in RotS, Anakin asks him as to whether it is possible to “learn this power” (referring to Plagueis wanting to keep himself alive), and Palpatine responds, “Not from a Jedi,” intentionally grinning at us, the audience.
And I won’t even touch that.