Feeder schools only have meaning in the context of a specific medical school, or a class of medical schools. For instance, the top undergrads are obviously feeders into the top medical schools - some more so than others. At the top schools, the schools' undergrad programs are also big feeders into their own medical schools. This is where going to a place like MIT or Princeton might be disadvantageous because there's no "home field" advantage when applying to med school.