As many folks have pointed out, the standard for medical clearance can't be zero risk -- or we'd have no pilots. Because older people have more health issues than young ones, tightening the standards would tend to force out experienced pilots. Of course, not every medical issue is age-related, not every experienced pilot would be replaced by an inexperienced one, and not every experienced pilot is safer than every (relatively) inexperienced one. Nonetheless, any proposal to tighten the standards would need to consider the offsetting safety effect of reducing the overall experience level of the profession.
The risk exposed by this incident is the risk of adding a couple of mechanical joints to an aircraft that already has thousands of them. Perhaps there should have been better oversight and mitigation of this risk, but that doesn't seem to be a reason to have denied clearance to this pilot.
If there'd been an incident resulting from a need for the pilot to have two fully functional hands, that would have been more disturbing. Perhaps there is a risk along those lines, but if so, this incident didn't expose it.