A puppet being operated by the real villain?
But why have a dime store Palpatine if the plan all along was to use the real thing?
Because that’s how Palpatine operates. Masks, deceptions and lies. Snoke was just a more sophisticated version of wearing a hood and keeping his face in a strategically placed shadow.
That’s a nice in-universe explanation, but in reality it’s almost certain, that JJ intended for Snoke to be the big bad, and when RJ dispatched him, they had to bring back Palpatine in some form to up the ante. Had it been their intention to bring back Palpatine, they would logically have introduced him as the puppet master in a cameo at the end of TLJ. Additionally RJ clearly made TLJ with the intention to break free from what came before, whilst TROS seems to do the opposite promising a whole host of connections to the past.