If this were true, there would be only one chef in the world (the person who is best at being a chef), only one baker, one software engineer, etc.
I don’t think this follows; in particular, following the policy “everyone does the thing which they are best at in the world” doesn’t actually make a prescription for most people, since most people are not the best in the world at anything (unless you take a weirdly granular view of things, like “the best Orthodontist named P. Sherman, with an office at 42 Wallaby Way, Sydney”, at which point the reductio stops seeming obviously absurdum)
Overall this is a good point, but I have one nit:
I don’t think this follows; in particular, following the policy “everyone does the thing which they are best at in the world” doesn’t actually make a prescription for most people, since most people are not the best in the world at anything (unless you take a weirdly granular view of things, like “the best Orthodontist named P. Sherman, with an office at 42 Wallaby Way, Sydney”, at which point the reductio stops seeming obviously absurdum)