I think there is some nuance that is missed when performing studies that compares hours practiced to mastery. I'm currently reading a book called A Mind for Numbers (the companion book for the popular MOOC on Coursera called Learning How to Learn) and what I am realizing is that not everyone practices or studies the most optimal way.

"For example, the number of hours of deliberate practice to first reach "master" status (a very high level of skill) ranged from 728 hours to 16,120 hours. This means that one player needed 22 times more deliberate practice than another player to become a master."

Maybe those 728 hours were more efficient and effective deliberate practice than the 16,120 hours.

Edit: the book is called "A Mind for Numbers", not "A Mind for Math"