b) PNF doesn't work through ROM
c) elbows are 3 joints away from the knee, and a shorter lever just means its easier to run.
d) you have less injuries thru sheer luck or undertraining.
the objections to overspeed or assisted running are that it is impossible to increase leg turnover or stride rate while being pulled!!!! You have to increase stride length to maintain the pace. For Elite level sprinters the difference is minimal because of the laws of diminishing.
Why not stick to 1K or 800m repeats at faster than race pace for 2-3 the distance? It's much more specific.