I was referring more to the actual fighting styles themselves being a product of their goals- the Soviet long range, pot-shotting, footwork heavy style is pretty optimal for international amateur competition, whereas the heavier infighting component of Western systems will be more useful in pro ranks.
You are 100% right about the reason for the underperformance of so many promising Cubans and Russians though. I think I remember reading some interview with Odlanier Solis or his coach where it was pretty explicitly stated that he got fat and undisciplined because he wasn't mentally equipped to handle the event of ice cream being available all the time.
On a side note from another thread, i really hope that fate doesn't fall on vasyl Lomachenko. that kid is amazing to watch and I'll be sorely disappointed if he tanks as a pro