I am doing backend in Kotlin, but I must admit that Java has been catching up quickly, and it seems like Kotlin has been shifting its focus to Kotlin Multiplatform. Modern Java is a good, pleasant language and a safer bet.

Gradle with Kotlin DSL is nice, what's annoying is Gradle's constant API reshuffling for the sake of it that breaks plugins. Some plugins also introduce pointless breaking changes just to have a fancier DSL.

The IDE support is not an issue in practice, in my opinion, because IDEA is the best IDE for both Java and Kotlin. The official Kotlin LSP was released 6 months ago, but I haven't tried it.