GWT is/was a terrible amount of overhead baggage, but had some brilliant event systems and DOM tricks for its day.
And the Java server code compiles to JVM bytecode. Languages often compile to some other form to run, and the fact that the compilation target is different for different parts doesn't change that the programming language is the same.
GWT is very much alive and kicking, but it's primarily used on internal business applications with large and complex code bases. And what overhead baggage are you talking about? GWT is designed to reduce overhead though cross-compiled, browser-spesific builds, dead-code removal, and js-optimizing.
Vaadin is consistently rated one of the best web app frameworks. Why its not more widely known is beyond me.