Actually there is no proof that anyone other than Kas'Im mastered all seven forms, let alone the saberstaff and jar'kai style as well.
Now Kas'im definitely has this.
'Within the first few passes Bane knew he couldn't win. Kas'Im had trained his entire life for this moment. After years of study, he'd mastered all seven forms of the lightsaber. Then he'd honed his skill for decades, perfecting every move and sequence until he had become the perfect weapon and the greatest living swordsman in the galaxy. Maybe the greatest swordsman ever. Bane was no match for him.' - Pod, Pg. 244.
Now this passage makes it pretty clear that noone had mastered the art of the saber to such a high degree like Kas'im had.
'He knocked once softly, careful not to wake the others. Before he could knock a second time, the door swung open to reveal the Twilek... The Blademaster's highly tuned reflexes had reacted to the first knock so quickly that he had already crossed the room and opened the door by the time the second rap came.' - PoD, Pg. 144.
This passage shows just how quick his reflexes really are.
'Bane hung his head and lowered his blade in an admission of defeat. The last pass he had held Kas'im off, but with each swing of his saber he and grown a microsecond slower. Fatigue was setting in. Even the force couldn't keep his muscles fresh forever, and the seemingly endless duel had finally taken too great a toll. The Blademaster, on the other hand, had lost almost none of his speed or sharpness' - PoD, Pg. 159.
This passage makes it clear that physically, Kas'im >>>>> Bane, and Bane was in very good physical condition himself, having spent most of his early life working on the gruelling mines of Apatros.
I think it's pretty safe to say that Kas'im's superior mastery of the saber and incredible physical condition would put him above Yoda.