"more productive" is not a singular metric. What indefinite 15% year over year growth in mainstream tech requires is (in addition to favorable market conditions) the ability to get useful work out of huge numbers of very inexperienced people.
Clearly Scheme, for instance, cannot do this better than Java. But this tells you next to nothing about which tool is more productive in the hands of a small team of people who know what they're doing.
This has been tried, usually driven by academics who try to start a business by hiring "elite" coders with the belief that you need many fewer elites to do the same work as "normal" coders. Sometimes they have short-term "hits", but it's usually not a sustainable business model. For one, it takes coders with some business sense and team skills, something the academic type tend to lack: they are idealists who get snagged up on arcane design philosophies. Imagine a room of Sheldon Coopers. I'm just the messenger.