have you tried it? Have you actually gone out and built something in Java using the latest in available JVMs and libraries and done user experience testing on the result?

Of course you haven't. Your preconception of what would happen is all the proof you think you need.
Of course your lack of experience with Java also means you'd be unable to create that Java application to be optimised for performance, which is another problem for a new tool to gain acceptance in an established industry.