I agree that GDP and other outcomes are another approach - and perhaps more accurate and more easily measured. GP suggested tech innovation might be an "interesting counterpoint" to conventional population/GDP approaches.
Innovation from China too... though I have the impression the government managed to lock-down dangerous (to the government) innovations, like gunpowder and flight, so I think progress would have slowed there, too.
I'm not aware of any particular efforts to suppress or restrict it beyond the usual Chinese restrictions on weapons. Wikipedia says a (non-central-government) militia official demonstrated a particularly effective form, and that there was later a restriction on trade of sulfur and saltpeter, but that appears more to build up their own stocks.
Err.. they had manned kites if that was what you mean? Marco Polo say to foretell whether a ship should sail, a man would be strapped to a kite having a rectangular grid framework and the subsequent flight pattern used to divine the outlook. That does seem to have been particularly restricted.