> Is there empirical evidence proving that Go is better than Java for small command-line apps

Sure. It doesn't require warmup, it's a little easier to deploy as a standalone executable, and performance is comparable to compiled Java code in programs of this size (you can easily confirm all three claims); those are pretty much the relevant requirements from many command line programs. It's not a property of the language but of its implementation choices (AOT compilation, statically linked runtime), which match the requirements of those kinds of applications better.