It answers the question: you can't just look at gross native memory usage and conclude the Java app is 100x less efficient, that value simply doesn't tell you a lot. Server VMs are commonly configured to use gigabytes of RAM from the get-go, and when the initial VM heap is full, Java will not make small adjustments but instead grab a big chunk, and when that is no longer needed, it is often reluctant to release that additional memory.

I have no doubt that a Rust app will generally be more memory-efficient, but ultimately for server applications that is really not something a lot of people care about because of the incredibly low cost of "just buying more".