There are a lot of good points here. I'll bring up a related concept.

I was listening to the interview of a professional soccer player some time ago. I can't remember who. Anyway, the athlete said that in soccer, it's 20% mental and 80% conditioning. After I thought about what he said, I admired the athlete for how much that statement made sense. Soccer is unlike basketball and unlike football. Perhaps in these others sports, an out-of-shape bench player might come into the game and make a difference at their position because they have lots of "heart". It struck me that you can't do that in competitive soccer. If you aren't fit in competitive soccer, you will be too winded after 20 seconds to be of any use, and you'll be a huge liability to your team. I remember sometimes trying to play competitive soccer as a youngster without being fit. It's basically impossible to do much of anything.

I draw the soccer analogy to survival. Different survival situations call for a different set of skills. I think anybody who tries to argue against the premise in the original post is being at least somewhat defensive. Depending on the situation, being fit may mean the difference between life or death. I have the ability to be in great shape, and I will try harder to be so. This thread provides yet more motivation. Thank you for reminding me.