What point are you arguing here? That it’s more difficult to be a doctor than an NFL player? That is highly subjective depending on what one finds “difficult”. For instance my dentist in SF and even primary care or dermatologists don’t have very stressful jobs and although they had many years of schooling, they didn’t have to subject their bodies to the intense and unrelenting physical rigor of first HS football, THEN college football and then the NFL. I would say for low level or intense stress maybe surgeons, oncologists, anesthesiologists or cardiologists have more stress day to day but that’s just my subjective opinion as well, as to them it may be as easy as flying a kite.

So what do you consider difficult? Having a linebacker smash into you at a full sprint over and over in practice and then not choking in a real game? Or studying relentlessly, writing grants, doing essentially free work as a resident for years while being on call. They are just stressful in different ways, but again, different humans have more fitness for one or the other.