That's the theory but it isn't that trivial to measure engineer's productivity, especially in small +/-20% range we're talking here. We aren't like bricklayers

That's the theory but it isn't that trivial to measure engineer's productivity, especially in small +/-20% range we're talking here. We aren't like bricklayers where you can directly and precisely measure the output. That's why in practice google's famous "20% time" is 120% time and on other hand it also has a lot of coasters working at half pace while cashing in 100% pay.