Edit: @jagthebeetle: have you tried "advanced mode"? (One should read the documentation before using it, it's really a game changer but requires one to read the docu first)
Closure is really a great compiler, it's just a shame it doesn't interact well (that is, at all) with the modern JS ecosystem.
Within Google, CC is heading towards being a an optimizing backend for other less painful languages such as Typescript (tsickle) and the yet-to-be-released J2CL compiler.
CC does pretty well with these examples (our debugger is not quite as flashy): https://closure-compiler-debugger.appspot.com/#input0%3D%252...
I actually considered musing about something like this in my post. Typescript support would be very interesting.
Fwiw, the tooling support around the CC has been a problem historically. We relied on Plovr for a long time, but eventually it fell unmaintained, and there wasn't an alternative for a lot of the relevant parts (e.g. gathering source files you care about). Some important dev features also just didn't quite work as intended (sourcemaps) for a long time.