Excuse me, If I sounded offensive in my last post. It's true that I do not like what Darth Sidious represents and politic on other side, but I am trying to be objective more than prejudiced. Palpatine's intellect is unquestionable. He managed to accomplish what he did(destroying jedi order and rule for 2 decades) due to his cunning, manipulation and foreseeing abilities. His servants and the clone army actually took out the jedi, he did not do that by himself (he did not kill Yoda and Anakin helped in defeating Windu, we can not be sure what could have happened if Anakin was not there). From my point of view he is coward, hiding behind his mask and let others do his plans. However its the Force might we are speaking about here. In that matter it is not necessary to be sith to accomplish what he did, anyone with superior intellect and strong will could do that (he could have wiped out Yoda and Windu with setting up precise traps, as we know even Yoda was not that wise and he did many mistakes in his judgements; and yes not only force sensitive beings could have impenetrable mind).
The Force represents raw power as it is in the nature, not politics. So let us concentrate on the force powers here and compare Kun and Sidious by their force abilities.
The facts we have about the lightsaber's skills of Kun and Sidious are in favour of Kun. Palpatine killed Kolar, Tiin and Fisto because they underestimated him, they were too confident that 4 of them could handle him without many efforts. So his skill with the lightsber and his quickness surprised them in that moment. So YES he had advantage, but not entirely based on his lightsaber skill.
Kun on the other hand invented his double-bladed lightsaber and had his own combat style. He was able to repeatedly defeat fellow students Crado and Sylvar in practice duels. He defeated ancient Odan-Urr, by Odan-Urr stating that his skill in the force and lightsaber can not match Kun's. Exar Kun killed his master Vodo-Siosk Baas, who was extremely skilled in the lightsaber combat, "With minimal effort". And Kun did not do that by surprise. He had the balls to state his beliefs and go in fair open fight.
Nomi Sunrider led thousands of Jedi against Kun to be able to defeat him but even then not entirely. And Darth Sidious allowed some cripple(Vader) to throw him in the shaft. He should have known so far that love is Vader's weakness and he should presumed that in the very moment he is killing what is left of Padme, which was Vader's biggest tragedy. So we have here stupidity, overconfidence, arrogance, all of it being weaknesses.
Kun possessed Freedon Nadd's amulet. With it Kun's power in the Force became extraordinary. With his Force Blasts he could crumble stone walls and crush bodies. Palaptine got his lightning but as it was stated in the post above he needed some preparation for it. The way I see it that Sidious will last like... 1 minute versus Kun in a straight fight.
Exar Kun survived for more than 4000 years. Kun could travel at will anywhere on Yavin 4, and was capable of enhancing others' Force powers (as when he helped Kyp Durron recover the Sun Crusher). He retained mental command over his Sith alchemy creations, which had survived from 4,000 years ago. His spirit form did not limit him from attacking others directly, as he burned Gantoris to death from the inside out and summoned two-headed bird like creatures composed of pure dark side energy, to tear Luke's body apart. Kun was also able to attack Corran Horn - in the guise of Keiran Halcyon. Horn believed that Kun could not affect the physical world and to prove him wrong, Kun used the Force to melt the detonators attached to the explosives Horn had brought and proceeded to assault Corran directly with the force, both physically and mentally.