I don't believe this stuff at all. Your average AP student has better study habits than Evariste Galois, and about a 0% chance of understanding Galois theory by the age that he invented it (19).
The same is clearly not true in mathematics. The modern regime of math practice, which involves lots of schoolwork, homework, tutoring, and other regimented practice, has not left 19th-century standards in the dust. The achievements of Galois would still be utterly extraordinary today. The notion that sports-style "deliberate practice" is universally beneficial towards a vague notion called "expertise" is simply not true.