Java's gotten a lot better and maybe some day in the future I'll go back to general purpose java for server-side development, but there's enough velocity increase in Kotlin that I feel more and more productive. The real victory of the language IMHO is absolute null awareness (at least for largely Kotlin codebases). This makes any sort of nullability issue perfectly clear as long as you're not '!!' (null-safe opt out) everywhere like a lunatic (or as a newb when I started). Being able to seamlessly weave java and Kotlin in the same projects has made the slow iterative migration a lot simpler as well. All the same dev toolchains/ecosystems, just a different compiler plugin.