macOS 27 has had, and still has, quite a few strange UI glitches and moments of sluggishness, even on fast Apple Silicon Macs.
Given how much UI behavior changed and broke during the beta cycle, I suspect Apple may have reworked a significant amount of the UI using Swift and Swift Concurrency.
Could some of the remaining sluggishness be caused by priority inversion or other concurrency problems, where UI work gets delayed even though the machine has plenty of performance available?
If macOS 27 is exposing weaknesses in Swift Concurrency when used at this scale, could that lead to changes in the concurrency model in future Swift releases?
Can you identify specific situations where you're seeing issues that would lead you to believe that Swift Concurrency is being used? (I'm not sure that you could determine that to be honest).
Apple employees are going to direct you to file feedback directly with Apple.
A lot of the UI broke during the macOS 27 betas, so they were probably rewriting large parts of it in Swift. And the strange occasional delays make me suspect priority inversion since my m3 MacBook Pro is plenty fast and has 24 GB of memory. There is usually no swapping in my usage.
You'd really need to provide specific examples — "A lot of the UI broke" and "they were probably rewriting large parts" aren't specific enough for anyone to be able to advise on anything.
Anecdotally, I've been using macOS 27 and it has been fine for me on my M3 Max-based laptop (excluding the expected set of bugs that surface during developer betas).