Interesting. When we started Codename One we wrote the UI for the web interface in GWT. It was awesome to work with but it was hard getting the "native" stuff working. E.g. mixing in custom JavaScript and getting the CSS look and feel right. Eventually we moved to bootstrap for the UI and now use Codename Ones JavaScript port for the UI.
We use react on typescript in Lightrun and it's an absolute pain for me personally. But it does have the advantage of wide skill set in terms of hiring. That's basically what it comes down to. I wish technologies like GWT would get better PR and traction but I'm not sure how we can get there.