At my previous job, I implemented a stream processing solution in Clojure, which superseded a Java one which never had quite worked (it was a pretty bad codebase, in fairness), added more complex functionality, and allowed me to drop 1/3rd of the code in that module (from 18KSLOC to 6KSLOC). More importantly, it worked as intended, and only a couple of negligible bugs made it to production, which for the complexity of the system, and the scarcity of QA we had, was surprisingly good, tbh.