I wouldn't call Xcode slim. It currently sits at 13GB+ as installed on my drive, and that does not include the simulators which are, what, 10GB each or something? Xcode is by far the largest application I have installed on my "daily driver" Mac.
It's still compressed on disk, so it takes only 5,4 GB of space, not 13 GB+. Sure, the simulator and the iOS or the other SDKs will take more space, but those aren't needed to develop macOS apps.