Is that an up-to-date critique? Because iOS 17/MacOS Sonoma have the rewritten JSON decoder:

> The code in our GitHub repository 20 has indeed shipped as part of iOS 17 and macOS Sonoma. That includes our new, dramatically faster implementations of JSONDecoder and Calendar.

https://forums.swift.org/t/any-updates-on-the-new-foundation...

That comment was from Nov 2023, and if you look at the GitHub repo, you’ll see that the JSON part of Foundation has commits within even the last month (perhaps getting ready for Swift 6.0?).