Earlier quoted context omitted.
I also question the universality of it. No amount of exercise changed my depression or made life any less miserable. Anti-depressants finally helped me get past the trauma I was unable to properly process otherwise.
I'm a non-competitive athlete, and yes exercise can help depression, but no, it will not be sufficient for anything but your mild to average case of it. Exercise is a crucial part of dealing with it, but it is not a panacea.
Exercise forms the foundation of a biologically healthy brain which is required for all conditions. For some conditions it’s all you need for others it’s not enough