[bzbarsky]

Think from the point of view of a tools/productivity engineer at a large company.

Yes, you invest some of your time to create the faster tool. Then hundreds to tens of thousands of people all use that faster tool to save time, day in and day out.

Just to put some concrete numbers to this, if you have a 100-person engineering team and you ask one of them to spend all their work time ensuring that the others are 1% more efficient than they would be otherwise (so saving each of them 5 minutes per typical 8 hour workday), you about break even. If you have a 500-person team, you come out ahead.

Now it's possible that the switch to a compiled language we are discussing would not save people 5 minutes per day, or that you don't have 100+ engineers. Obviously for a tool that only the developer of the tool will use the calculus is very different!