Is it stupid that Rey is going to beat Darth Sidious in single combat?
I thought he died in Return of the Jedi...
He did. Disney is not the real canon, it is disgraceful...it is fraught with inconsistencies and poor, bland creative choices. Anything halfway good they do is stolen from the older movies and de-canonized material and changed slightly.
The trailers for the last movie reveal that Sidious has returned in Disney's canon. Relatively reliable plot leaks claim that Rey is literally going to defeat Sidious which is impossible.