Where is the circular reasoning? There are a fixed number of hours in the day, and I presume that becoming elite at either a mental level or a physical level, for most people, requires focus for the majority of your waking hours. My assumption may be wrong, but I don't see any circular reasoning. Note that I say that I think most people can achieve a good general level of fitness.

As far as my own issues go, I think you're speaking from the perspective of someone who has no medical issues and assuming that everyone else is similarly healthy. I have rheumatoid arthritis and hypermobile ehlers-danlos syndrome (amongst other problems). I try to keep fit, have special shoes and joint supports, do everything my physiotherapist tells me to do, and I exercise fairly intensely for at least an hour a day. But ultimately, I have physical limits that despite continual medical intervention, have proven resistant to treatment besides painkillers. In the last month alone, I've been to hospital 6 times. There's a good chance I won't be able to walk more than a few hundred metres by the time I'm 30, and currently if I try to push myself too hard, I typically end up injuring myself and needing to go to hospital.

A computer, for me, and other people like me, can be one of the most transformative purchases of our lives. On a computer, nobody knows you're disabled and you can do almost everything that an able-bodied person can. Arthritis can be a problem, but heated gloves help a lot with that.