Nobody has ever used Ruby because he thought it might be faster than Java. Java primarily competes against C++, not against “scripting” languages like Ruby and Python which have significantly shorter edit-(compile)-run cycles. Each of these languages also have unique features that are difficult or cumbersome to model in Java (functional programming, metaprogramming, modern object systems).

I do not doubt that there can be cases where a transition like Python → Java can make sense, but it would be silly to assume this would generally be a good idea.