Despite some surface differences, Kotlin and Java are so similar that "losing" one to the other isn't really that big a change. They run on the same platforms and they use the same frameworks, dependencies, debuggers, and other tooling.
A Java developer will pick up Kotlin much faster than, say, a Postgres developer will pick up Mongo. It takes a lot longer for a Java programmer to learn the Android environment than the Kotlin language.
If there were a trend from Java towards Rust or Go or Python, that would be a significant change in the world. If Java were to vanish tomorrow and everybody had to pick up Kotlin, the world would be pretty much the same in a week. Kotlin is nice, benefitting from a clean-sheet implementation of lessons that Java takes on only with difficulty, but it's not a wholesale break.
They are tools used by programmers. They do, in fact, have languages of their own, but more to the point they have whole ecosystems of expected behaviors, idioms, best practices, etc etc etc. Those take longer to learn than a programming language.
Similarly, "web app" isn't a programming language, and neither is "server side". But they are toolkits that a developer must learn on top of their programming language, and it takes longer than the actual language itself.
A Java developer will pick up Kotlin much faster than, say, a Postgres developer will pick up Mongo. It takes a lot longer for a Java programmer to learn the Android environment than the Kotlin language.
If there were a trend from Java towards Rust or Go or Python, that would be a significant change in the world. If Java were to vanish tomorrow and everybody had to pick up Kotlin, the world would be pretty much the same in a week. Kotlin is nice, benefitting from a clean-sheet implementation of lessons that Java takes on only with difficulty, but it's not a wholesale break.