Actually you may not have much Kotlin experience on server side.

Those features you mentioned not exists in Java, JVM is another topic, many Java features does not known by JVM as well.

99% of the most popular libs just works as expected under Kotlin.

Generics are not good in Java as well, thanks for the type erasure. But Kotlin's covariance and contravariance is way intuitive and more useable.

Also Kotlin's coroutines works well (with Reactor for example). The code is cleaner, especially if you build reactive system.

The Android community is bigger but Kotlin is the main language on Android. This is similar as I say do not use nodejs be application (actually i dont like it :D ) as most of the developer useJavaScript for frontend . Actually server side community is also huge and growing constantly.

Scala's compatibility with Java is far worse.

Where I would not use Kotlin is JEE apps. But on cloud/ms... side it is way better.

Also in containers JVM itself is crap.

Of course this is all just my experiences.