your son needs to look into how the pre-med committee (which these schools likely have) operates at each school. This can be one of the dark sides of college admissions, colleges that aren’t particularly selective in admissions that have amazing med school admission rates. It might look at first like they are working miracles, but the truth is a bit harsher. As Richmond says
Med schools know which colleges have committees, so the lack of a letter is pretty much an automatic deny.
While Richmond is more forthcoming than most, your son should still check about the evaluation process there. After all if anyone can get a letter but they write “not recommended” in it then there is no sense in applying so they can control who applies thru that lever. Some schools do exactly this, one college used to say “The Committee’s level of recommendation and the tone and content of the letter to be written is disussed (sic) with applicants as openly as possible.”