I'll throw my take into the mix.
...even if he was so far above the caliber of other Jedi (no evidence to support such assumptions)...
I'm gonna have to say you're dead wrong in this case.
Darth Vader in Episode III was just beginning to unlock his potential. The Emperor clearly thought that Vader would some day be more powerful than he. And remember, Anakin was about 5 years of training behind other Jedi and still one of the best. Between AOTC and ROTS it is clear he is still growing in power. And in TPM, it is clearly stated that Anakin's raw power is greater than any Jedi in recorded history ("...his reading is off the chart...").
Vader clearly had the ambition to become the Emperor, as he told Padme, Luke, and probably his secret apprentice. Whether or not Vader would have been able to rule is obviously subject to speculation, but I like to think he would have, not because of him being intellectually or even emotionally capable, but because his abilities with the Force would have grown to unreal levels. I think if he had ruled, he would have been able to use some form of battle meditation- even untrained- to be able to turn events in his favor 100% of the time. Plus, eveyone in their right mind would be terrified of him.
But clearly, it was not to be. His own arrogance destroyed all of his potential before it could even blossom. That's my take.