Working both smarter and harder has the best chance of leading to success.
The article missed another major point... if you were the smartest person in the world and studied harder than anyone else, but you picked an unmarketable field of study... you are not likely to get ahead. My brother's kids all got degrees in “environmental science” because they all believe that “global warming” is going to destroy the world. For some reason none of them have managed to get a decent job.