The dynamic typing is optional. E.g. at the startup I work for, the convention is to use static types for function signatures, and dynamic types within functions.

In general though Groovy/Grails is actually surprisingly good. Groovy is much easier to learn that Scala, more powerful than Python, and most Grails conventions are fairly straightforward and easy to understand. Both Groovy and Grails are a little bit under documented, which is frustrating, but not so bad as to be a deal breaker. That said for my personal projects I use Python/Django, only because the community is much stronger. And although I do miss Groovy's closures, the strength of the libraries and ecosystem, as well as the fact that it's easier to hire developers, more than make up for whatever syntactical advantages that Groovy has.