I suppose if all things were indeed "equal," I'd agree. And yes, I think linkages are the #1 reason to attend a top formal postbac.
But even if we take linkages out of the equation, let's consider the non-trad you mention in your last sentence. This individual can attend a postbac program at either Columbia or Goucher/Scripps/Bryn Mawr. Columbia is surely the superior undergraduate institution versus all three of the others. Its postbac program has some semblance of linkages, but as you say, this individual doesn't care. Some students cruise through Columbia's postbac and get into good medical schools. Some do not get accepted. Many drop out before they can even finish. The top three formal postbac programs boast 100% acceptance rates to medical schools. Thus, acceptance to one of these programs (as you say, they screen for top applicants) is as close as one can get to a "guarantee" of med school admission.
Which path should the individual choose? They can go to the bigger-name school and have a moderate chance of med school acceptance, or they can go to Bryn Mawr/Scripps/Goucher and have, essentially, a 100% chance of med school acceptance.
Point is, statistically speaking, medical schools clearly prefer the non-linking non-trad from BM/Scripps/Goucher to the one from Columbia. So, the smart student, having the option of going to both and there being no real difference in cost, should attend the latter.