In my own experience gradle is far simpler than SBT, especially when you factor in the binary incompatibility between scala versions and the technical debt this adds to your build plugins.

Plus compilation with SBT is ridiculously, laughably slow. Modifiying your build.sbt essentially causes a rebuild of your whole project. The complexity and expressiveness of SBT is a BAD THING in terms of compilation and troubleshooting.

Maven suffers from a different issue. Build processes are fundamentally procedural, not declarative so sooner or later you have to shoehorn your shell commands into a maven plugin section in your xml instead of just executing them as a line from within your build script.