I don't think the comparison is very good. Brosmer seems to have a little better arm, throws with anticipation better (at least so far), and make the smart play a more than YOLOing. Keenum got away with a lot of bad decisions that season for the Vikings and was more of a risk taker than Max seems to be. I would say Max is probably more on the Brock Purdy mold of QB. He's going to go out there and be accurate, make the right reads, and throw with good timing, but not going to be throwing a lot of flashy balls and wow you that way. Interestingly, JJ McCarthy is a lot that way too but is more physically gifted than Brosmer. JJ has a bigger arm, slightly bigger and more athletic..ect.
But if I'm KoC I like the idea of having a guy like Brosmer on the roster that can probably step in and play QB with the same mentality as JJ. Both are really sharp minded for football, good leaders, the kind of QBs people will follow. I don't think you would have to change the offense much for Brosmer other than JJ has more experience with it.