I agree with you. I think may be the time to market using other technologies than java may be lower. But is there a substantial difference in productivity using Python/Node.js / ROR over Java?
That totally depends on a number of factors. I'm more productive in RoR than in Java because I don't have to type as much--but I'm not that familiar with the newer Java web technologies, so I'm biased.
Hugely more productive? Probably not; modern Java web development is pretty speedy, and the tooling (primarily IDEs) are better for Java because of its relatively static nature.
