This is not an improvement from lack of GC per se but rather from zero cost abstractions (everything is monomorphised, no sin such as type erasure) first and foremost, and yes, deterministic memory management. Java is the worse language if you need to push performance to the limit since it does not offer convenient lower level language constructs to do so (unlike C#), but at reaching 80th percentile of performance, it is by far the best one.

But yes, GC is very much not free and is an explicit tradeoff vs compile time + manual memory management.