Your theory hinges on “The Emperor is sooo powerful/evil that he…” which is lamer than shit.
He’s so powerful/evil that he can use force lightning. How is that lamer than shit?
Darth Vader is a top tier Force Wielder.
Nothing in the OT indicates this.
To say that he can’t use Force Lightning because he’s somehow inept in comparison to Sidious is to claim Sidious is akin to a God which is lame.
Except I said neither of those things.
Less powerful /= inept
More powerful /= God
My simple theory /= lame