Gradle is undoubtedly slower. However it’s at least 10x more capable of doing various things around building your app like testing, building images, publishing, etc. Like if I needed to build, fat jar, test and publish a multiproject repository I would almost certainly want to use Gradle over SBT.

But Gradle is probably a bit overkill for a single entry point small app that does one thing and has minimal testing needs (though it can certainly do that!). You wouldn’t bring in a dump truck whenever a pickup would work just fine.