> My understanding is that Java added a lot of functional programming

This is true, but needs more context. Java 8 added Stream API, which (at this time) was a fantastic breath of fresh air. However, the whole thing felt overengineered at many points, aka - it made complex things possible (collector chaining is admittedly cool, parallel streams are useful for quick-and-dirty data processing), but simple everyday things cumbersome. I cannot emphasize how tiring it was to have to write this useless bolierplate

  customers.stream().map(c -> c.getName()).collect(Collectors.joining(", "))

  customers.map(c -> c.getName()).join(", ")

Sort of true, but I often hear this take from Java programmers and it feels like "Blub" [1]/Stockholm syndrome to me.

Personally, I'm extremely glad to not have had to write .toStream().map(...).collect(Collectors.list()) or whatever in years for what could be a map. Similar with async code and exception handling.

For me one of the main advantages of Kotlin is that is decreases verbosity so much that the interesting business logic is actually much easier to follow. Even if you disregard all the things it has Java doesn't the syntax is just so much better.

[1] https://paulgraham.com/avg.html

At least where I work, writing new Java code is discouraged and you should instead use Kotlin for backend services. Spring Boot which is the framework we use, supports Kotlin just fine, at the same level as Java. And if you use Jetbrains tools, Kotlin tooling is also pretty good (outside Jetbrains I will admit it is worse than Java). Now, even in new Java projects you can still be using Kotlin because it is the default language for Gradle (previously it was Groovy).

My org had to write a pivotal backend service on the JVM, due to JDBC having the largest number of data source adapters.

The choice was Kotlin. Scala is too "powerful" and can be written in a style that is difficult for others, and Java too verbose.

Kotlin is instantly familiar to modern TypeScript/Swift/Rust etc devs.

The only negative in my mind has been IntelliJ being the only decent IDE, but even this has changed recently with Jetbrains releasing `kotlin-lsp` for VS Code

https://github.com/Kotlin/kotlin-lsp

Java did indeed add more FP to the language, but Java's type system is still fairly primitive compared to Scala's.

Java's new features are always going to be on paper. The ecosystem, with all its legacy code, is always going to be a decade behind. And if you are starting a new project, why would you pick Java over Kotlin?