TheOneOfMortis
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Tzeenth you keep bringing up how good a duelist they are well here is point to consider. Never mind Kas'im mastering all of the forms. the very fact that he is a high level master of Maskashi, the style tailor made for 10n1 lightsaber duelling, should alone give him a huge advantage over Obi-Wan's Soresu, as Soresu is most effective (in lightsaber srtting) against defending against a barrage of attacks and tiring out the opponent and then waiting for them to leave holes in their defence, it has no real advantage agaiants Makashi's fencing stykle of swordsplay, likewise Makashi is the best duelling form but with a weakness to explosive offensive swordplay, which Soresu is not.
So Makashi alone imo would be a very bad match up for Obi-Wan's Soresu. Then take into account that Kas'im can primarily use a Makashi centered attack against Obi-Wan (of which he is high level master), but then also can employ techniques from the other forms as well that dont themselves pose any weakness to Obi-Wan's Soresu but might be effective depending on the circumstances of the fight at the time, plus the added vsriety will disfragment Obi-Wan's precognition.
So I really don't see why you think Obi-Wan possesses the technical advantage as a dueller.
Then, as Zamp as others have pointed out, Obi-Wan possesses no real advantage in Force power to overcome Kas'im's superior swordplay, if anything he is weaker, hence Kas'im is a lightsaber specialist and he has focused his force powers on things like speed, strength, reflex etc as well as defenceive force use, and he has great credentials in all of these things, he tanked Bane's attack, and as Legend pointed out his speed and stamina etc are always talked veyr highly of even though it can be hard to know exactly how fast etc.
So I really dont see why you think Obi-Wan's average Force prowess and high level mastery of Soresu makes him better than somebody with Kas'im's superior Force prowess, high level mastery of all forms, and hence superior variety, precognition advantage, and ability to tailor his style to expose weaknesses in Obi-Wans and ensure his own possesses no vulnerabilities to it.
And if you want to argue feats, I dont see how Obi-Wan defeating a bunch of newbs like Opress and Assaji Ventress, a non-force powered cyborg like Grievous, a stagnant and crazy sith lord whos skills have atropophied over decades like CW Maul, or what most people like Lucien think is a fluke victory over Anakin (who at the time really hadnt gon very far at all in achiving his potential).
Kas'im defeated Bane using advanages Zamp, I, Legend and others have been talking about, and say what you will but Bane at this stage was a progidy and extremely powerful force user, certainly more impressive than newsb like ventress and opress. He also killed his master when he was younger who was apparently veyr powerful (a sith lord, not a newb like ventress and opress), and had lots of war experience and combat against Jedi prior to working at Academy, where he practised his skills every day.