For example, I would think that the best Java engineers are probably much more productive than the best C++ engineers. However, the market is probably full of poor Java engineers that the average Java engineer is probably a lot worse than the average C++ engineer.
C++ is such a complicated language that if you are a professional C++ engineer and still employed, you must be fairly skilled. So, for example if you start a tech company or an open source project it might be better to choose C++ as the implementation language even though Java might make you more productive.
Funnily enough, Linus does not apply this logic to C vs C++ debate and has come to the opposite conclusion : http://harmful.cat-v.org/software/c++/linus