Thank you for the informative article.

I have two things I would like to explain:

1. GWT: in the core it is just a Java2JavaScript transpiler. So this is just like TypeScript2JavaScript transpiler. Google use today the newest version of J2CL (Java2Closure transpiler). Check out my newest article about this stuff: http://bit.ly/WebJavaStory GWT/J2CL is very up-to-date and not legacy.
2. Google needs to support GMail for Web browser, Android and iOS. They use Java for presentation and business logic. For Web browser they use GWT/J2CL to transpile from Java to JavaScript. For Android they can directly use Java and for iOS they use J2ObjC (Java2ObjectiveC https://developers.google.com/j2objc). So they reuse a lot of codes in Java for different platforms.
3. In GWT they built the optimizer of JavaScript directly in the transpiler. In J2CL they use Closure to optimize JavaScript. Today you can build the same webapp based on Java and transpile it with GWT or J2CL to JavaScript. Here is an interesting discussion: https://groups.google.com/d/msg/Google-Web-Toolkit/xWW57bMWKmA/RMKOn6rhAwAJ

Thanks, Lofi