Our use case is definitely a pathologically bad problem for Java's GC. Nevertheless, it is a real use case, and CPU and GC are the primary impacts to our service.
You mean you're actually seeing 90% GC overhead and are not looking to improve on that? (like by tuning the GC or changing your implementation). GC impact on normal behaving applications should be less than a few percent, so you're not comparing Rust and Java, but Rust and badly written/tuned Java - which doesn't say anything about the maximum attainable performance.