10k at competitive times builds the stamina required to run out a full game of football. Its building the base so you can do the repeat sprints. Beep tests are great as well and there is multiple facets to it, I agree but nothing beats kilometres into the legs on a regular basis.Eh. I actually kind of disagree. A 10K run is not really transferrable to a game of football. Players will also rarely train in a way that reflects this level of endurance. Hence why clubs prefer the yo-yo test as a mechanism, because it involves short bursts and very short recovery times, reflecting the running style you'll see in a game of footy. Training is much closer to a hybrid of anaerobic/aerobic that tests both energy systems, such as repeat 400m sprints.
Yes the best kids are athletes, but that's true with almost every modern sport.