Bahamut.Celebrindal said:
»Spend a lifetime around such folks and you end up seeing its just those raw hours alone in a practice room or gym that differentiate those who succeed and those who over time give up. There's no voodoo, there's no shortcuts. And the athletes and artists all know this and are just laughing at the general public thinking they've found out some secret unknown for centuries. Go ahead and keep thinking all these foolish paths...it just makes it harder for those outside the inner circles to get work in these fields.
I don't think anyone on any page has said that just doing one thing will make you competitive with an expert who has years of dedicated training in the field. It feels to me like you're inserting words that aren't there, perhaps because you feel there's been disrespect toward people who train judiciously to become the best at what they do.
It is a biological fact that differences in hormone levels will effect your mental state, and an indisputable fact that your mental state has impact when you are aiming to perform at the highest level. No, someone who hasn't ever practiced music will not compete with YoYo Ma. But, the idea that because someone is excellent at something, they're doing everything right, is reductive and contrary to all science imaginable.
Practice(and in some cases genetics) will be the largest contributors to success in effectively any discipline. But, that doesn't mean the small contributors/detractors don't exist. Look at the differences in records now versus the same events a century ago. Those wouldn't be possible without the greater understanding of nutrition and physiology being used to condition their bodies to an absolute peak. But, someone a century ago would've shrugged off things like that as irrelevant, too.
Edit: Specifically in regards to visualization, you cannot practice most things 16 hours a day physically. But, you can use visualization during downtime to continue building the mental component of your performance if you were so inclined. Michael Phelps practiced in the pool for 5-6 hours, 6 days a week. He
also used visualization for 2 hours a day. It's an additional contributing factor, it's not a replacement for the physical practice.