To me the whole point of Kotlin is fixing all the things that are wrong with Java lol

But idiomatic Kotlin is still too close to Java, they call it "direct programming style" and it's basically already obsolete

Null safety is great but the way they've implemented it with weird syntax like ? and ?.let is not great, it would have been a lot better to just have a regular Maybe type in the native library from the start. Like sure the nullable type is in some ways functionally equivalent, but it doesn't implement map, flatMap, applicative etc like a Maybe does, and when it behaves like it does, it's mostly kind of by accident, not by any real understanding of those operations (and, fatally, it's completely disconnected from map, flatMap etc on lists etc - those should be interfaces that everything that can be mapped, flatmapped etc on implements, not methods that get hurr durr added here and there, sometimes as a regular method called map, sometimes built into the compiler called let)

They've completely dropped the ball on error handling - they don't even know themselves whether the language or people using it should use sealed classes, exceptions or their shitty Result class (which, again, this is a solved problem, they could have just included Maybe, Either, Try etc in the native library from the start)

Coroutines and structured concurrency are powerful but their API is so extremely confusing and full of footguns that virtually no codebase using them ever uses them correctly to reap the benefits

I could go on - don't get me wrong, I love a lot about Kotlin and it's a massive massive improvement on Java but it's not a great language unless you run it with Arrow and learn to completely sidestep large parts of the language (just like you had to do with Java)