You are right ... It does not need one, to be Smart ... in the usual sense of high school grades. Being a good doctor, is in one joining the ranks of those ... with the Mission, of serving humankind ... it is not a money making Profession.
The Average Student, provided he or she has the Knack ... meaning, the willingness to learn, and the "Sixth Sense" is usually a better doctor than the Smart ones ... who, are generally, unable to timely diagnose due to the vast "data" at their disposal.
The first thing, is to learn the Basics ... meaning, get the MD, and then proceed, humanely, with the Practice.
And it is always a good thing, to Consult your reliable Doctor friends ... when in doubt, about your diagnosis or Prognosis. And to be good, is in one, always remaining a good learner ... learning, and experience, makes the Great Doctor ... Ego has no place in Medicine.
But since a doctor is dealing with someone else's health and life ... learn to be 100% sure, before taking any random action.
In Practicing Medicine or anything, there are Times, when things have to be done first, and thinking done later... the Average do it by instinct, rather than by starting to read the American Medical Association's Journal, while the patient is dying.
Briefly, Average guys make Good Doctors ... while the smart ones go to Pharma Multinationals, and vie for Prizes.