The Groovy is slow argument has sort of run out of steam in my opinion. Support for invok-dynamic and the static compilation annotation provide a lot of speed. I use Groovy daily and my experience is anecdotal but maybe it is time to do some benchmarks of my own.
Dynamic-mode Groovy is as slow as other dynamic languages. The recently added static-compilation mode for Groovy still regularly spews up bugs, perhaps because it was written by a single programmer with little beta testing whereas Scala and Java have many high-pedigree developers behind them, and heaps of documentation and testing.
