I regard Swift's inconsistent runtime performance and over-reliance on compiler optimizations as a major problem with the current state of the language.

It does not help that some slowdowns are due to bugs, and some due to questionable implementation details that require knowledge of how the runtime operates.

Of course, knowing about the runtime is necessary for all micro-optimization regardless of language, but Swift currently requires it almost all of the time.

The difference between Swift and ObjC/C is glaringly obvious.

Your GCD wrapper examples use only the simplest form of generics, with no constraints at all. Magnify the problems you had to get this to work by x10.000 and you get how easy it is to do anything complex with Swift's generics. It's a maze of missing features and bugs.

I think it's very understandable that Owens got fed up with it.