For example, 70% of inbox.google.com web app is written in Java and transpiled into JS. And front end is written in Closure. Inbox Android app uses the core as it is while iPhone app transpile the core via J2ObjC. Google Drive Spreadsheet, Calender are also built with this combination. I think Google values GWT not because it's good front end framework, but because of its power to share the code across different platforms.