I didn't ask you whether or not Kenobi was "the" master of Soresu (I hope you realize that even if he was "the" master, he would still be "a master", anyways), True Jedi. I asked you to prove up on the assertion that Kenobi could defeat the battle master of the New Jedi Order, who's just as experienced and quick thinking as Obi-Wan is, as well as more innately skilled with a broader knowledge of and focus on saber combat.
But, here's another question: what does that even mean being "the" master of Soresu? He wasn't a lightsaber instructor. He didn't create Soresu. There's no proof that he was even close to the best Soresu practitioner in history, or even in his own era. Being "the" master of Soresu doesn't mean you could beat "the" master of the fast, medium, and strong styles of the New Jedi Order. As far as I can ascertain, all it means is what it says: you've mastered Soresu. Congratulations! Besides, I recall Mace Windu being the only person who stated such a thing in a private, philosophical pep-talk between the two.
I could throw some spin on that last sentence, too. Mace considered Obi-Wan as "the" master of Soresu, not because he was the best Soresu duelist, but because he epitomized Soresu's core belief: to defend. Notice how Mace Windu says [possible paraphrase] "be who you are and Grievous will never defeat you". Who is Obi-Wan? He is a Jedi. Mace was saying be a Jedi, upholding the virtues of the light side, only rising to fight to defend (key phrase) against injustice done and evil cannot overcome you. That is what the Jedi belief is. They don't seek battle, nor to kill. That's why Mace Windu asks Obi-Wan, "I am called a great swordsman because I invented a lethal style; but who is greater: the creator of the killing form or the master of [Soresu]?".
Obviously, Mace Windu would ROFLstomp Obi-Wan, but Windu implies that he's the lesser of the two because of the difference in their form's philosophies. The entire reason for Obi-Wan switching to Soresu was because he wanted to defend his fellow Jedi from death; that's why he may be considered "the" master of Soresu because his intentions were completely in line with Soresu's philosophy, as well as the Jedi Order's.
The status of prodigal son of defensive lightsaber combat?
That's wunderbar, but no more meaningful to what I was asking than a ham sandwich. Try putting that into the context of this thread, or a particular point about a saber duel between these two.