I haven't played Undisputed, but the problem with all of the old MMA games is that the controls to actually make grappling meaningful just aren't there. Technically even striking probably can't be adequately controlled. Take Fight Night, for example. FN has very solid controls and allows you to more or less do what you want, but it uses every button and both sticks, and only covers Boxing. Now add kicks, knees, elbows, clinch work, and grappling, and there's an obvious gap between available inputs and expected outcomes.
In the end, you end up with a lot of "canned" animations (even if the transitions are fluid) that just feel like bad RPS and not actually fighting.
Then there's the obviously asinine design decisions where they allow things like top-game wrestlers even *having* moves like knee bars and footlocks, and it just hurts the overall feel of the game for true fans.
Edit: And I know it was a typo. =p