Productivity is basically the amount of output in a given timeframe. I believe Deep Work is essential to achieve high productivity.
With respect to software engineering, there are two sources that improves productivity: tooling and Architecture. Effective tooling for software development can only make an Engineer 2 to 3 times more productive than the average. When we talk about 10x Engineer, we are most likely referring to the productivity gains from making right architectual decisions. From a business perspective, it could literally save months or even years of work.