I just think the MCAT is such a different beast from any course or test. For example, I missed a perfect score on the organic chemistry ACS by 1 point, which put me in the 100th percentile nationwide. I took the toughest Ochem prof at my school and aced her class. I went on to become an Ochem tutor for my school. Of course, I knew the basic background information needed for the organic chemistry portion of the MCAT, but the manner in which that information was asked for is wholly different from the way any of my courses or even the ACS asked me to regurgitate it.
The MCAT typically asks very simple questions....as long as you decipher what the question is really asking. This is a skill I feel you will only get from doing MCAT passages. Yes, there is a percentage of the MCAT that is pure rote memorization, but I think those questions are usually such esoteric knowledge that you will either know them or you won't.