Whatever your opinion may be he is confirmed to be a Niman user and he turned it into an utterly chaotic brand of Niman.
That was Kun's style:
Some unique objects are invariably associated with their remarkable owners. The unusual double-bladed lightsaber of the fallen Jedi Exar Kun is one such artifact. This weapon as distinctive and dangerous as its builder, the Dark Lord of the Sith, who initiated the great Sith War and nearly toppled the Old Republic.[...]
As the battle against the Jedi escalated, Kun altered his normal lightsaber into a more deadly and dangerous weapon. Kun added a second emitter matrix on the opposite end of the handgrip, allowing him to release two blue-white blades simultaneously. The dark Jedi wielded the saber much as he would a quarterstaff, using one blade to block incoming attacks, then quickly spinning the handgrip to use the second blade to strike a killing blow against his opponent.
Customized controls allowed him to adjust each blade's length from half a meter to one and a half meters. Panels controlled each blade's intensity: at its highest setting, a blade was like any other lightsaber, with the ability to cut through dense materials such as armor plating and durasteel with virtually no resistance. At the lowest power setting, a blade became a simple shaft of light, delivering no damage and providing no resistance against incoming lightsaber attacks. By abruptly shortening a blade or dropping it to the lowest power setting, Kun tricked his opponents into overextending themselves during attacks, giving him an opportunity for a dealy counterstrike. By coupling these tactics with his Force abilities to predict the actions of his opponents, Kun became virtually unstoppable in combat.
- The Essential Guide to Weapons and Technology
Yet Ulic was a master duelist, the greatest Jedi of his day and one of the most powerful Sith in history:
While his brother [Ulic] perfected his combat skills by defeating training droids, Cay was more interested in putting the dismantled droids back together.- Power of the Jedi Sourcebook
Ulic Qel-Droma quickly mastered the art of lightsaber dueling.- The Complete Star Wars Encyclopedia
"Ulic was once our greatest Jedi Knight. Now he is our greatest shame."- Sylvar
But Ulic Qel-Droma isn't just anyone; he's a Jedi, perhaps the greatest of his time.- Star Wars: Tales of the Jedi: Dark Lords of the Sith #5 Solicitation
The spirit of Freedon Nadd appeared before Ulic and proclaimed he would one day become one of the most powerful SIth Lords in history.- Power of the Jedi Sourcebook
So Revan learned what Meetra Surik did, sweet. Where did he learn Juyo again? Because Surik mastered it via Master Kavar, the other forms from the Jedi High Council members and Kreia, not just the out-of-shape Dantooine Jedi Enclave that had not been the same since Vodo's death.
Warb Null was very powerful and highly skilled, his Dark Armor only boosted his prowess:
Warb Null-The leader of the dissident Naddist, Null combined martial prowess with his mastery of the dark-side of the Force. He was eventually killed by UIic Qel-Droma.- Straight from the Horse's Mouth: A Guide to the Tales of the Jedi Universe, Part 3—Star Wars Insider 28
Ulic kills three Krath warriors, causing a trail of green energy before engaging Null, completely outspeeding him:
Mandalore the Ultimate left a greater legacy through his neo crusade than Mandalore the Indomitable, a comment which was made thousands of years later by the way.
Revan fought Ultimate on a bridge, compared to Ulic fighting Indomitable whom had a Basilisk war droid and fired it at Ulic, whom uses Force Barrier to tank the incoming fire, which has destroyed military fortifications and damaged capital ship hulls, casually:
Ulic himself had chains to stand on:
If you want to go by character POV however:
"Freedon Nadd_was a Dark Jedi. The stories say he was_far worse than Revan and Malak_ever were." ―Xarga
"Exar Kun was a far more powerful Sith Lord than any who have come since. The very ground trembled beneath his feet and when he looked at you.... you just....." - Knights of the Old Republic
Just for the record, Freedon Nadd has knowledge of all Force techniques everywhere and is far more powerful than Naga Sadow:
"Eventually, the apprentice[Nadd] became far more powerful than the teacher[Sadow]..."-The Official Star Wars Factfile 90
"Freedon Nadd has knowledge of all Jedi and Sith Force powers presented herein as well as those abilities still hidden in ancient Holocrons and tomes."―Tales of the Jedi Companion
Exar Kun was even more powerful than Freedon Nadd:
Once the most powerful and dangerous of the Dark Lords of the Sith, he was responsible for the deaths of millions four millennia before the rise of the Empire. Killed by an overwhelming force of Jedi, the spirit of Exar Kun survived across the vastness of time to challenge Luke Skywalker and a new group of Jedi trainees.
- The Complete Star Wars Encyclopedia
Cay and Ulic dueled and Ulic came out on top, because he was better and stronger, which is considerable given Cay's own considerable powers:
The Qel-Droma family has produced many powerful Force sensitives. Some, such as Cay Qel-Droma, have been shining examples of the strength of the Force. Others, like Cay’s brother Ulic, have fallen prey to the temptations of the dark side.- Knights of the Old Republic II: The Sith Lords: Prima Official Game Guide
Exar Kun was absolutely superior to Vodo Siosk-Baas in that contest:
In the process he once more faced his former master, Vodo Siosk Baas, this time armed with a double-bladed lightsaber of his own construction. Master Vodo did not have a chance, and fell to his former student.
- The Dark Side Sourcebook
The two fought, and Vodo-Siosk Baas was no match for Exar Kun's double-bladed lightsaber.
-Power of the Jedi Sourcebook
Infact Exar Kun was far more powerful than Ulic Qel-Droma, Vodo Siosk-Baas, Thon, Arca Jeth, Odan-Urr, Nomi Sunrider or any one Jedi of his time:
though Kun was far more powerful than any one other Jedi of the time, A combined force had defeated him.
-The Jedi Academy Sourcebook
This is extremely impressive considering the great feats of the Jedi of his time, chaostheory has excellent respect threads on that front:
http://www.comicvine.com/profile/ct123/blog/vodo-siosk-baas-respect-thread/107346/
http://www.comicvine.com/profile/ct123/blog/odan-urr-respect-thread/107353/
http://www.comicvine.com/profile/ct123/blog/arca-jeth-respect-thread/107414/
As well as Nargaroth's Thon respect thread:
http://www.comicvine.com/profile/zapan87/blog/
Perhaps most impressive is Thon controlling and banishing the greatest amount of Dark Side energy, the Jedi had ever recorded by that point:
Exar Kun being far more powerful than him is an extremely impressive accolade.
Revan's lightsaber knowledge/style is most well pointed out by Drew Karpyshyn, certainly greater than fanon theories on the matter. On that matter Drew claims Revan is primarily a Niman user but uses all forms, which is likely where you got the idea of his using Juyo. Unfortunately he still lacks any solid evidence for Revan being a master duelist, beyond character POV (ehich will shoot you in the foot) and Drew's opinion.
Comparatively Exar Kun is a great master duelist:
Kun was a master of lightsaber combat and had even bested Master Vodo’s quarterstaff during a sparring practice.- Power of the Jedi Sourcebook
An excellent student and a master swordsman, Exar Kun was fascinated with the powers of the ancient Sith Lords.- The Dark Side Sourcebook
Both Jedi are master swordsman-- neither can claim an advantage with the lightsaber!
-Tales of the Jedi
Exar Kun is infact ambidextrous in the weapon's use:
He is also a high tier master of the saberstaff and Jar'kai:
Gnost-Dural also believes that Kun was unparalelled in the lightsaber prowess he achieved:
As a young Jedi Knight, Exar Kun exhibited a strong connection to the Force. Through long practice he achieved unparalleled prowess in lightsaber combat.- Gnost-Dural (Star Wars: The Old Republic - Timeline - The Exar Kun War)
I see no evidence suggesting Revan increased in lightsaber skill, only Force power.