What effect does the range of a squat play on the architecture of a myofascial unit?
I think squat ROM can have tremendous lengthening effects on posterior anatomy train in a very functional / integrated manner. In fact, I notice that emphasizing deep squats often clears up issues for athletes who do not have appropriate hip mobility to sprint efficiently. More specifically, those athletes who always have trouble getting the knees up and running with big front side mechanics almost always see HUGE benefits on running mechanics just from deep squatting.
Is there any difference in sarcomer length or the area of muscular development?
I don't really understand what you're asking here.
I've seen studies that suggest isometric training is only relevant +- 10 degrees of the joint angle being worked.
This is largely true. Isometric strength gains tend to be specific to 10-15 degrees surrounding the position trained. This doesn't apply to this discussion though because we're not speaking of isometric contractions. Also, as I noted in a previous point, the hip joint does move in to similar positions of flexion in sprinting to what is observed in a deep squat. This occurs during both acceleration and maxV sprinting. During maxV sprinting, I'm again referring to when the knee is high and in front of the body and the athlete is aggressively accelerating the thigh down toward the ground.
When I do a A2G squat the last third of the action seems to be nearly irrelevant as the load isn't high enough to challenge me through this range and any attempt to maintain the same power output sees it basically turn into a jump squat, but basically i don't feel that it helps me on the track, yet I feel 1/2 and 1/4 squats do.
I think part of the discrepancy of opinions is believing that only the final third of the range of motion of a squat is relevant or important. I think there are a litany of benefits to squatting deep that far outweigh the fact that the final 20 degrees are sub-maximal. Not to mention that this final range of motion is worked in practically every other activity you do from walking, running, plyos, etc. while the positions of greater knee and hip flexion are pretty much ignored (at least as far as overload goes) in training.