Groovy was never the problem (Groovy has types, always had, you could use them if you wanted).
Think about it: what do you do with a build tool? You write a little recipe, then you run it. Does that remind something? Yes, it reminds scripts, like bash scripts you run all the time in your terminal. And why are scripts almost universally written without types... and no typed alternative, of which there are many, has caught on? Because if you're just going to modify a script and immediately run it, while keeping it short enough so you can know what it does without reading a book, how does adding types help you? Quite to the contrary, scripts (including build scripts) should be small, and having types all over the place make it far more verbose than it should be, likely pushing it out of your comfortable local memory in your brain, at which point you need something akin to a "real" programming language and a compiled program, not a script. Larger programs benefit from types because you don't just run the program, make changes, and run them again, like you do with scripts. You write them, test them, compile them, package them and finally you distribute them to your users who hopefully only need to configure them, not modify their internals. If your build is that complex, that's exactly what you should be doing instead of trying to shoehorn types into your scripts and expecting them to look like real programs.
Also, the Kotlin DSL just doesn't assist in the most problematic aspect of Gradle: its total lack of discoverability. Try doing something on your Kotlin Gradle file using a plugin you're not familiar with (which is all of them for most of us). It's completely impossible unless you know the DSL of the plugin, just like it was the case with Groovy... Once you know the DSL, it's fairly easy, but even in Groovy you will get auto-completion once you've got to the DSL "entry point", no need for Kotlin. I've been saying this since before they introduced the Kotlin DSL, and now i feel completely vindicated. I've never met anyone who told me "Gradle is so much easier now with Kotlin". But it did mess up plugins I wrote in Kotlin as now Gradle has a dependency on a very particular version of the Kotlin compiler, and God help you if your plugin was written with a different version in mind.