Regrettably all a current medical certificate is useful for is knowing
that the recipient WAS fit to fly at the time that they took the
medical. Half an hour later, who knows.

It's actually a little better than that. Since you must report all
medications you are taking, the medical examiner can assess if one, or a
combination of several medications, might impair your coordination
and/or judgment which could affect your ability to act as PIC (or to
drive a car for that matter).

On the other hand, the AOPA is fond of (correctly) reporting that there
is no statistical correlation between a pilot having a medical
certificate and accidents due to medical causes.

Tony V. LS6-b "6N"