Yeah the Java way makes sense if it's the only thing running on that machine, or at least you know ahead of time how much RAM to budget to each thing. Which was often the case on servers. I'm not surprised if that performs better than Go in a way, but seems like Go does ok. If they really wanted a custom heap on top of preallocated memory in a Go program, couldn't they just do that?

The weirder part is that Java also used to be a bigger thing client-side, back when websites commonly included Java applets.