There's a huge difference in how much intrinsic athletic ability matters depending on the sport. It's a bigger factor in a sport like baseball or tennis where eyesight and coordination are so critical; you can only train those things to a limited extent. But for sports that rely more on strength and endurance than technical skill pretty much anyone has the potential to reach a high level of performance (not Olympic level but like NCAA division 3 level) regardless of intrinsic ability. It's mostly a matter of being disciplined and grinding out the workouts every day for years.
Don't kid yourself. I can tell who is and isn't a good athlete from 50 yards away just by how they walk. Hard work matters, but its more about eliminating those with talent rather than allowing those without talent to compete favorably. Also, its a self reinforcing cycle. You have talent, you win, winning is fun, you work harder to win more, goto step 2.
PS The cutoff from HS to college sports is about as extreme as the jump to the pros...its less than 1% each time.
