I recently took to rewriting what should be a very simple app from Obj-C to Swift with SwiftUI - because it's the future. The CPU usage was at 5% while idle, just for having a simple tiny pie chart that updates. Not to mention that for some seemingly basic things I still had to use AppKit anyway.

Wrote basically the exact same thing 1 day later in Swift with AppKit and NO SwiftUI and it sits at 0% CPU usage with less code complexity. Maybe in a few years I will give SwiftUI another try.