I'm not sure if he can beat a magnaguard, granted a standard Magnaguard may not be swimming in feats either.
A supposed master who "studied" every facet of lightsaber combat theoretically shouldn't be driven back, resort to sabotaging training, and dying to a trainee. This could honestly go either way. I'd wager the Magnaguard for a majority, but Kas'im can probably take a few rounds via using the force. He is most likely outskilled though