>>76377002 (OP)true. if you can run 5k at a decent pace thats all you need for fitness. we arent endurance hunters anymore, you dont need to run 15km while spear hunting a wounded deer. youll never need to run more than 5k in daily life, its exponentially more fit that 90% of the population, gives you ample cardio for gym, sex, and daily life. its also very doable and simple to attain. anyone can do it in a couple months.
doing more obviously confers more benefit, but 5k as a standard length for everyone to train and stay there if they want? that sounds good.