My hometown I believe ticks all 4 of the things you mentioned. So I agree with you that genetics is a minor part of the equation
This is a personal anecdote of mine:
I lived in 3 nations: Sardinia ( hometown ), London and Vilnius. I do a lot of running and I love collecting data, something I noticed is that every time I go back to my hometown my VO2 max starts skyrocketing, after training as little as 3 weeks in my hometown it goes up by more than 10 points, when I go back it starts declining slowly until it goes back to slightly above the value when I left.
I do believe there must be something special about the environment, I do continue working from home when I'm in my hometown to stay longer, so it is not an holiday effect, my diet actually goes worst when I go back home because I go a lot to restaurants that I missed. And even with worst diet my fitness improves fast ( I run faster with same HR ( even for a while when I'm back ), VO2 and race predictor improves drastically), my stress goes down and my sleep score almost maxes out ( 98/100 )