Your competitiveness for a specific medical specialty and a specific residency program will depend, in large part, on your Step scores. Step scores are correlated with undergraduate GPA and MCAT score combined. We know that undergraduate GPA and MCAT are not randomly distributed among medial schools but that some medical schools matriculate students with higher averages compared with other schools (the basis for using the
LizzyM score to target medical school applications). So, if Step 1 score is a major factor in getting into a specific residency and LizzyM score is a predictor of Step 1 score and correlated with the medical school(s) is admitted to, the big predictor of whether you'll get into a residency is not the medical school attended so much as it is good Step 1. The school attended is an intervening or confounding variable (always get those two mixed up).
There might be a bit of a bump obtained by having a Dean's letter from a feeder school rather than a non-feeder school for a specific residency program but, as have been shown, it is not impossible to get into any residency from any medical school. The other confounder is that some schools are very mission driven and are good at selecting students who meet that mission. If that mission is primary care, then students will preferentially be headed toward primary care residencies rather than derm and ortho even if they had the step scores to be successful in matching into one of those specialties.