I don't believe that this is true. Because, one can just write simple Scala and has pretty much everything that Kotlin has (minus its nullability magic) and never deal with these edgecases. Even compiletimes are decent then.

But with Kotlin, it is actually enforced that the more advanced features of Scala are not available, so it makes sure that compiletimes etc. stay short. It also simply reduces the burden of the IntelliJ devs, because it's not just "Language -> IDE" but IDE capabilities impact how the language is designed too. And having a good IDE is very important for productivity.