It's 100% as useful, but much more difficult to mock and inject.
Isn't it just the opposite?
The whole reason of Mokito ( https://site.mockito.org/ ) is to make Java mocks easier by adding dynamic typing.
If I have a type system that prevents certain classes of defects, I gleefully accept that bounty.
If I have a type system that simplifies certain classes of tests, I gleefully accept that bounty.
I will happily rant and complain about all of them, but I will also try to program to the strengths of what I'm using. Wishing one language was a different language is a waste of everyone's time.