lol what's on the exam is far from excessive. It could be so, so much worse....
This is the MCAT in a nutshell. Everything they do, and I mean
everything is a scaled down, simplified version of the science compared to what they could test and what many see in undergrad.
The new emphasis on the MCAT reflects the changing face of medicine. I am ~ 5 years removed from med school and even now, the education and integration of research, technology and medicine grows each year. The scope and scale of clinical research is huge and is getting bigger. Even physicians who do not go into research (most of them) need to be able to read understand, analyze and assimilate up to date research (clinical, surgical, pharmacological) throughout their career. Why is it all chem/bio/biochem? Because that is all most pre-meds have. You have not gone to med school, you have not had the extensive MD/DO level coursework in anatomy, physio, pathology, pharmacology, psychiatry, histology, etc.... They can only test you on what they know most student have had or should have seen in undergrad as they prepared for medical school admissions. This is limited to the basic sciences (Chem, Bio, Biochem etc..).
You are not a physician yet, heck even after you graduate you don't feel like one yet. The AAMC cannot test you on that high level medical knowledge. You may not see it now, but many of these skills/concepts they are testing you on WILL show up in med school. I had many times through MSI and MSII where I thought "Oh, that's why the AAMC cared if I knew X." It's not a perfect exam but the AAMC feels it's the best way to gauge your capability for handling the material in medical school.
Hope this helps. Good Luck!