Red Nemesis
wut?
You pointed out the exact reason why I wanted to know Bane's relative skill.
RN
As I remember, Bane memorized the forms well enough to match Kas'im when the later was using a weapon he was familiar with. Bane was winning the first half of the fight largely because he knew everything Kas'im could do with a saber. This came from hours upon hours of time spent dueling, but also hours spent memorizing specific forms and the "combinations" of those forms.
As I mentioned earlier, Count Dooku claimed in Labyrinth of Evil to General Grievous that he could demonstrate maneuvers and techniques from all of the standing members of the Jedi High Council and inflict them in assaults against the general.
Despite this, and the fact that Dooku was once one of the Temple's foremost combat instructors, no source states that Count Dooku is anything other than a master of Makashi, nor do we assume as much.
Darth Vader, in the Rise of Darth Vader, demonstrated a form unique and unprecedented to his enemies, borrowing techniques from all lightsaber forms.
Despite this, no source states that Vader is a master of anything other than Djem So.
The fact that he was able to competently stand against Kas'im does not mean that he is a Master of any specific form. As the narration concluded, Bane was winning solely because he was the more powerful Force user.
RN
Add to that his ability to teach Zannah whatever form would be most effective (implying that he could also have taught her Makashi, for example) it certainly seems as though Bane is competent to judge Kas'im. I will defer to someone with sources, however, if there is something I've overlooked.
There's no doubt that Bane was proficient in lightsaber combat, perhaps in all forms. But I asked you if he was a Master of any. It's rather like Assant's ignorant perception of Anoon Bondara. She is a trained Jedi Knight, she has presumably witnessed other duelists and instructors in action, yet concludes Bondara is the greatest duelist alive.
Other sources disprove this. Why is Bane's perception much more acute [when it comes to an objective analysis of Bane'sKAS'IM's skills]?