In an ideal world (which we don't have and likely never will), every person in every car would be feeding data to a central database (like waze) of driving conditions. Then the averages would be as claimed (more accurate than the fallible human). Unfortunately (if you desire such an accurate GPS guidance system) such is not the case.
At the present time, the data Waze uses is far to sparse (at least in my community) to turn over all my routing choices to it (if my goal is speedy transit between two points that I already know... over terrain with which I'm intimately familiar). The theoretcal world where the compter's math ability trumps unformed human navigation is a long way off (not because the math is faulty, but because the data is insuficcient.
Waze learns - and for that I'm greatful. I hope it's learning from others, and I sense that I've taught it a thing or two (by driving routes that are/were better than the route it suggested.