Kyle would win if it was the Dark Kyle, the only Sith to have been killed by a light jedi was Maul and he was a sorry git( also Jeric and Co. By Kyle),Luke didn't Kill the Empoerer , Vader did and in Mysteries of the Sith Nothing could beat the Evil Kyle.
Yes, I have to agree that Darth Maul was possibly killed a little too easily for a Sith apprentice. My understanding is that the Sith Lords are supposed to be more powerful than other Dark Jedi.
Jerec was simply a more powerful Dark Jedi - I don't think he was a Sith Lord, although he was probably well on the way to becoming one. Therefore, in those terms, Kyle only tackled Dark Jedi, whereas Luke tackled actual Sith Lords - the Emperor and Vader. Having said that, Luke would have lost his battle if Vader had not turned back to the Light to save his son.
And on a technical point, it could be argued that Vader did not physically kill the Emperor - he simply threw him down that shaft, which killed him. In a face-to-face battle, Vader would have lost against the Emperor - and in fact, he did, because he died as a result of the Emperor's Force Lightning in his weakened state. Luke certainly would never have prevailed against the Emperor if Vader had not intervened.