Making "a" process .01% more efficient is not sufficient in your example. You need (the weighted average of) everything to become that much more effective.
Somebody improving e.g. the build speed by that amount will not be paying back their salary in improved productivity of other developers. While a person who increases the click through rate on ads by 0.02% probably does.
If you find someone who can make things .002% more efficient and pay them $100,000 a year, you've still come out ahead.
At that revenue, it doesn't take much to get an ROI on a new employee.