>I realized that what I'd boiled it down to looked an awful lot like Rust code
you're no longer writing idiomatic java at this point - probably with zero object oriented programming. so might as well write it in Rust from the get-go.
If I'd started in Rust I likely wouldn't have finished it at all. Java allowed me to start out just focused on the algorithm with very little regard for memory usage patterns and then refactor towards zero garbage collection. Rust can sort of allow the same thing by just sprinkling everything with clone and/or Rc/Arc, but it's much more in the way than just having a garage collector there automatically.
you're no longer writing idiomatic java at this point - probably with zero object oriented programming. so might as well write it in Rust from the get-go.