Well back in the 50s plus the military had the highest standards for anything...including Police Officers....believe it or not.
At one time the military was the only place you could obtain an Instrument Rating.
At one time the Royal Military College turned down more physically and academically fit entrants than all the colleges and universities in the world.
It is former Military Pilots/ Persons that formed the Department of Transport in most or all countries, in Canada it is now known as the Ministry of Transport or Transport Canada.
Where does a pilot come from:
Grade School
College
University
A Flying Instructor at a privately owned school
A Bush Pilot
Air Cadets or any other Cadet Program
Does a pilot need an education?
To be honest it depends what he wants to do.
Fly for the Military or any Commercial Operator...Yes
To be a Bush Pilot it sure does not hurt to have some education...the more the better...like anything else

I think you can Honestly answer your own question....Does a pilot need good grades???
What is your answer as an employer or passenger'/crew member???
Cheers...Happy Landings...Doug