Kas'im himself is a very acrobatic fighter, nothing indicates her endurance is greater than his, and no one has even tried to say he'd one shot her.
I have no idea what you're talking about.
That being said, I do believe Shaak Ti would be the winner. After all, her skills with a lightsaber did lead to her victory over a master of multiple lightsaber styles, and her blend of Ataru and Makashi paired with leaping power attacks has been shown to be unorthodox and devastating. While she's not necessarily a better duelist than Kas'im is, (Or necessarily a lesser one,) I do believe these two would go toe to toe in a duel, and neither of them have any significant physical edges over the other.
The main edge Shaak Ti will have here is through her powers with the Force. We've seen Kas'im conjure powerful barriers and defenses to defend himself against Bane's assaults, but he seems to refrain from actually using the Force offensively to attack and seems to rely on his lightsaber prowess to overcome his enemies. On the other hand, you have Shaak Ti--Who subjugated an entire planet of violent creatures (Including Rancors and Saarlacs) with the Force, her lone presence negating the Dark Energies of Felucia. We've also seen her use her powers offensively, blasting her enemies with Kinetite and Telekinetic missiles, and she's adept into chaining these attacks into her lightsaber sequences.
Ultimately, Shaak Ti is the Bane of this argument--Only far more experienced.
