It depends on what you mean by "on the MCAT". If you mean there is a passage every so often that is biochem/cell bio/genetics/stats related you are correct. If you are implying that you need any knowledge about those subjects at all you are mistaken. I didn't take any of the classes you mentioned prior to the MCAT and whenever I got a passage relating to those subjects I found the questions either (A) had an answer that was directly in the passage or (B) were actually testing a simple basic science concept (phys/bio/gen chem/ochem).
Most of those topics (with the exception of stats) are already on the MCAT. The AAMC states this and lets it be known knowledge to whichever test-taker/applicant wishes to find out about the test:
https://www.aamc.org/students/download/85566/data/bstopics.pdf
However, these are all topics which are discussed over the course of a one year intro bio pathway. Having taken upper level classes may help, but sometimes can also confuse things, as they are testing fundamental knowledge from intro classes, or in some cases with more difficult passages: testing your ability to use introductory concepts in novel situations (topics and examples that may be covered in upper level classes or in more recent scientific literature.. and by recent I mean in the last 5 years, not anything cutting edge).
I'm not sure what result medical schools are hoping to achieve by wanting additional subjects on the MCAT. If its that they want more science knowledge out of their entering class, then just make those subjects prerequisites... The test has already proven to be an adequate selection tool for schools as evidenced by their high graduation/STEP1/2 pass rate.
I don't think the point is to increase pre-reqs or have students need to take these upper level classes. IIRC (and I didn't read the documents earlier in the thread because I think I read the AAMC's release a year ago when they and posters here first started talking about changes to the MCAT in the near future), they aren't looking to add more pre-reqs. They surveyed current and graduated medical students about what they felt were important topics in the first two years of med school, and what areas would having fundamental proficiency in would have helped them the most. I don't think this would require a significant restructing of introductory courses or of pre-req classes, it is simply shifting the focus on the exam to topics that may better assess applicant competency and predict success in the pre-clinical years. Since more and more schools are "recommending" or "highly recommending" biochem from applicants anyway, I think that may be the only subject that may become a pre-req, and honestly I don't think that would be a bad thing. Since most med students complain about biochem being their hardest subject in first year, I think having an introductory knowledge of biochem would be beneficial for entering medical students, to make the transition to the level of biochem in med school easier. This shouldn't replace orgo II, IMHO, but it would be a nice addition.
In my own personal experience, I was much more successful in biochem than in either orgo I or II. I felt that biochem helped clarify some concepts I may have learned earlier in orgo and cell bio, and also helped synthesize concepts from physio and cell bio by connecting the chemical/molecular level to the macro scale. As someone who did mediocre-poorly in chem classes but aced bio classes, I thought it refreshed concepts I had learned years ago in chem & orgo and especially put context to them, which ultimately helped my MCAT re-take.
I don't think biochem is necessary for an MCAT taker now, but if the AAMC focuses more on it, and if students routinely say they struggle in biochem in med school, then why not have students take an introductory biochem so they more students are on an equal footing regarding the terminology and basic scheme of biochem?
