Not sure why Ragnos is being brought up, it furthers the notion that spirits are far more powerful in their actual bodies. Though in the case of Exar Kun, the difference would probably be negligible.
[SPOILER - highlight to read]: still stomped NJO Luke tho
__________________ ”You presume limits to my power. There are none.”
IIRC Kun unlocked Kyp Durron's potential and told him to use the dark-side to stomp Luke, he didn't do it under his own power. Also the ritual that turned him into a spirit was supposed to make him more powerful. Anyways Tython, defeated more impressive foes and has good enough accolades to show that he can defeat Kun.
__________________ "Vader's pulse and breathing were machine-regulated, so they could not quicken; but something in his chest became more electric around his meetings with the Emperor; he could not say how. A feeling of fullness, of power, of dark and demon mastery -- of secret lusts, unrestrained passion, wild submission -- all these things were in Vader's heart as he neared his Emperor. These things and more."
Registered: Aug 2014
Location: The balance of the Force
Kun has just begun edging in on Streen when Kyp Durron arrives at the Jedi Academy. Kun immediately senses in the young man his ideal subject. Like Gantoris, Kyp is strong-willed and impatient to learn. Moreover, he is far more powerful than the Eol Sha leader, and young enough to be overconfident and naive.
Over a number of weeks, Kun slowly bends Kyp to his will, and begins to augment his power. He grows very powerful on Kyp's hate, and soon his hold on Kyp is so complete that he can send Kyp beyond the planet to do his will and still retain control over his subject. Ultimately, he has Kyp return to Yavin Four and helps him reclaim the Sun Crusher. He also bolsters Kyp's talents to allow him to defeat Luke and place him in a coma.
--Taken from the Jedi Academy Sourcebook
The systems hummed as they returned to life, charging up. Exar Kun had also been betrayed by his supposed partner, the warlord Ulic Qel-Droma. Now Han had betrayed Kyp. Master Skywalker had also betrayed him by failing to teach the appropriate lessons...appropriate defenses against Exar Kun. In his head the voice of the Sith Lord shouted for him to kill Han Solo, to destroy the enemy. To let his anger flow through and be strong. It overwhelmed Kyp. He squeezed his dark eyes shut, unable to watch as his hands gripped the control levers for launching the torpedo. He primed the system. The screens blinked with warning signals, which he disregarded.
He needed to destroy something. He needed to kill those who had betrayed him. His fists gripped the firing handles. His thumbs rested on the launch buttons, squeezing, ready—
Squeezing—
And then the haunting voice of Exar Kun rose to a wail in his mind, an utterly forlorn scream as if he were being torn out of this universe and exiled to another place entirely, where he could torment Kyp Durron no more. Kyp snapped backward in his control seat as if an invisible tow cable had been severed. His arms and head dangled like a puppet with suddenly snipped strings. The cool wind of freedom whistled through his mind and body. He blinked his eyes and shuddered with revulsion at what he had been about to do.
The Millennium Falcon still gripped the Sun Crusher in its tractor beam. As Kyp saw the battered old ship, Han Solo's prize possession, he felt a tidal wave of despair. Kyp reached out to the energy torpedo controls and vehemently canceled the firing sequence. The plasma generator flicked and faded as the energy died away. Without the presence of Exar Kun inside him, Kyp felt isolated, suddenly in the free fall—but independent.
He opened the communication channel but couldn't form words for a few moments. His throat was dry. It felt as if he hadn't had anything to eat or drink in four thousand years. "Han," he croaked, and said louder, "Han this is Kyp! I..." He paused, not knowing what next to say—what else he could say. He hung his head and finally finished, "I surrender."
--Taken from Champions of the Force
Kun was amping and controlling Kyp, these are not the only sources that say so either.
__________________
Within your furnace heart, you burn in your own flame. This is how it feels to be Anakin Skywalker.