I agree with your basic premise, but not the conclusion. Imo, I'm not sure "most people here" would necessarily have gotten into great law schools. As a simple case, consider the median med student--what are his stats? What kind of law school could he get in to?
As a quick and dirty way of analyzing this, if we assume the median medical student is the average student at the median school, we get an average MCAT (according to USnews) of about 30--roughly 85th percentile (according to USNews, the average MCAT was slightly under 30 at the number 71 ranked school out of 146), and an average GPA in the 3.6-3.7 range. According to USnews, the number 20 law school (GWU) had an LSAT range of 163-168 (representing the LSAT scores for the 25th percentile to the 75th percentile student at GWU). A 163-168 represents the 89th to 96th percentile of LSAT takers. The GPA range at GWU is 3.41-3.86--for the sake of argument, let's assume the average GPA is the average of this range, roughly 3.6 or so.
So, a quick look suggests that the median med student is medium-competitive for a top 20 law school--GPA is about right, but MCAT is a quite low compared to the LSAT equivalent--the median med student's MCAT is actually lower than the 25th percentile student at GWU (although you perhaps you could float the argument that the MCAT pool is "smarter"--not sure how true that is). This means they're far less competitive for a top 10 law school (the number 10 school, UVA, had an average GPA of 3.7 and LSATS in the 92-98th percentile).
But as you note, unlike medicine, the returns to law school are mostly concentrated in the top schools--no offense to GWU law grads, but I imagine their job prospects are not nearly as good the prospects for UVA grads, which probably still aren't as good as say, Harvard Law grads.
So I'm not sure "most med students" would have been able to get into the top schools (and thereby get the top law jobs)--this quick and dirty analysis suggests the median med student would have at least some difficulty getting into even a top 20 school--and that's the median student, to say nothing of the 40th percentile or 25th percentile medical student. The bottom line is that I don't think the median medical student "could have done better" if he switched to law--he probably ends up around the same or slightly worse (again, I'm kind of down on prospects for GWU grads, but I'm willing to be corrected). Students below the median are probably doing better in medicine than they could in law.
The general fallacy that seems to afflict people in the medical profession is "I made it through medicine--I'm smarter and harder working the average guy, so I should be able to succeed in any field (e.g. law, etc)." The first part of the statement is true--to make it through medicine, you must be smarter and harder working than the average guy. But the conclusion doesn't follow, because to succeed in any other field, it's not sufficient to be better than the average guy--you need to be better than a lot of other people who are really smart, hard working, and talented as well. In fact, the #1 law school (Yale) has stats (GPA 3.82-3.96, LSATs 98th-99th percentile) that are actually higher than the #1 med school (Harvard), with an average GPA 3.86 (so note the 25th percentile student at Yale Law is just a bit below the average guy at Harvard!) and an average MCAT in the 96th percentile. Bottom line is there's no "free lunch"--people who earn the kind of money people on this board want to earn are *all* (a) hard working, (b) smart, (c) talented, and (d) lucky (or at least some combination of these).