The article doesn't make really controlled findings. There's an argument to be made that the increase to diseases isn't purely lack of vitamin D but lack of exercise.

Our ancestors got lots of Vit D but they also got lots of exercise while absorbing the sun.

I still don't think it's going to be wise to go out and just bake in the high UV of early afternoons but rather it's important to go outside early to mid morning or late afternoon and absorb some sun without copious amounts of sunblock.