How about this:
at the elite level a good kicker can kick from his own 22 to well within the opposition 22.
So a big but aimless kick from own 22 that crosses touch somewhere around 1/2 way and is caught by defender 10 metres from his own goal-line puts the defenders at an unreasonable disadvantage as a QT will not lead to a gain in ground (in N/H).
Why take a quick throw 30-50 behind the line of touch to then just kick for touch? Tactically naive? if QT is taken to run ball back at opposition then I can see benefit but if (in your example) ball has cross LOT around 1/2 way then our throw in there is preferable to thier throw in potentially nearer our line! I understand your view is that the clearing kick could get much further but in reality the odds are against this.