You say, "People who are naturally something, like tall, or thin, are not privileged." Yes ... they are. That's exactly what privilege is. When one has done nothing but still has an advantage. In today's world being thin is an advantage.
Yes, there are people who work darned hard at getting fit. They are somewhat privileged in that their body type allows them to shed weight and gain muscle through physicality., and they definitely did something for it.
Guess what? There are also people who can get ripped without as much work as someone else ... they're even more privileged.
Then there are the people who work out six days a week and still carry an inordinate amount of weight ... not so privileged.
Also, all that hard work aside, naturally thin people are not necessarily fit, rather they are privileged to look a certain way that is valued in our society.
I am not judging anyone, nor am I envious. I had that privilege, without six hours in a gym, when I was younger. I am now 72-years-old, grateful to be healthy and fit (not thin), with a brain together enough to be able to coach others to better health.
Peace out.