I made this claim (single threaded performance matters) but in a parallel comment to yours noted that I was unable to find substantiating statements from apple

I made this claim (single threaded performance matters) but in a parallel comment to yours noted that I was unable to find substantiating statements from apple that I believe led to my assertion. So in that spirit I will point out that Apple's support code / framworks etc do a bunch of multithreaded UI and network stuff even when and app's code is putatively single threaded. Now that stuff IMHO is pretty high latency (e.g. waiting on user action) so as a developer I still think my statement, and your impression, are correct. But I'd like to see something from Apple on the topic.