I was just wondering about power difference between various versions of Sidious.
First, how much power did he gain between RotS and RotJ, and later between RotJ and DE?
Second, even if RotJ version of Sidious is much more powerful in the Force than his former self, does it also mean that RotJ Sids is a superior combatant? (Possibly he didn’t use his saber skills during his reign as an Emperor)
__________________ Theory is like a box of tools. It must be useful. It must function. And not for itself.
I believe the changes between RotS and RotJ weren't too big. For what he gained in force power, he lost in saberskills. Between RotJ and DE, however, it's a little harder to say. While his saberskills reverted to being better than in RotS, the only hugely notable way that his Force Powers seem to have changed is the fact that he could then summon Force Storms, his largest-scale ability, which gives him some major points.
Sabers: DE Sidious > ROTS Sidious >>> ROTJ Sidious
Force: DE Sidious >= ROTJ Sidious >> ROTS Sidious
Then there's the fact that DE Sids could create Force-Storms, which boost him a hell'a lot.