Productivity equals wealth and to first order a nation's (or business') economic productivity is its manpower, that is, more people is more productivity. If we make sharp and sudden decreases in our national labor force, we can expect sharp decrease in productivity and wealth.
That’s an irrational statement. If your statement were correct, companies would always be hiring and never outsource or have layoffs.
Productivity increases are achieved through technology advancements, on going employee training , better tools and procedures plus improved management process and a nearly endless host of other factors.