It’s a fair argument, but of the dozens of examples I’m personally aware of, from the tiniest and newest galleries to the very biggest blue chip ones, the 50% split basically never varies. The galleries compete on other things including attending art fairs (where many galleries do most of their sales), controlling access to networks of collectors, good exhibition spaces, money and assistance to send works to museums and other non-commercial shows which raise the artist’s profile, insurance and storage of works, fancy dinners after openings, and advances to cover production costs.

I know less about how the gallerists balance sheets look at the end of their careers, but I’d suspect that more of their net worth has come from having insider knowledge to make strategic acquisitions of rising stars (at 50% off sticker price) and then talking up their book, than simply accumulating what profits are left over from their 50% after paying for all of that.