I would think that Palpatine has an IQ slightly below average (90-95), but most people around him are dumber than him and are easily manipulated, plus the Jedi as shown in the prequels are no longer the ideal guardians they supposedly were before the prequels. So if anyone is born in the galaxy who is smarter than him, it would be a threat.

Maybe Palpatine invented the dumb prophecy about an akin bringing balance to the force in order to have his implies creation destroy the weakened Jedi order, because they are stupid enough to believe it.