I don’t think it’s necessarily the school when one is talking lower tier. I suspect it’s the MCAT scores. By the old scoring there was some correlation between ACT scores and MCAT scores. I recall seeing an article a few years back that said many scored within 2 points on these tests. If one had an ACT of 21 or 23, even adding 2 points (or 4) wasn’t going to give them that great of an MCAT score.
If one translates the new MCAT score to the old one, my middle son kept with the correlation, as have a couple of others I know of in person. Not many with high enough ACT scores get attracted to low tier schools. Those schools don’t work miracles.