Different medical schools have different missions and offer different opportunities. Harvard/ Johns Hopkins/Stanford are in the business of training academic researchers. These schools are looking for a very specific subset of students.
Those research-oriented schools may offer better research opportunities than San Juan Bautista or Meharry or NYMC, but which school produces better doctors? It depends on what flavor of “better” you’re using.
There are data that show that a MCAT score has a pretty high correlation with a student’s academic success in the first year of medical school. However, there is a poor correlation between MCAT scores and a student’s success in clinical rotations.