Interesting. Although this point of view might be a bit simplified, there's another example of a weapon, which was both relatively cheap to make - and really hard to use unless the whole society was built around the skills required to use it. Mongols! Light cavalry using composite bows was both unbelievably effective and hard to copy for everybody but steppe nomads. All Mongols were hunters, they practically lived wi…
Also, light cavalry armies are useless against castles and fortified cities as the ones found in most of Europe, specially when you don't have huge, flat battlefields that allow light cavalry to circle any target.
In other words, Mongol warfare was perfect for the environment they were created for: vast empty dry lands with few geographical features and settlements which are far from each other.