I used to be a kernel developer at Apple starting in 2006. Internally, every alternate major release was exactly this. All common paths were identified, and most of the dev time on the release was spent on optimizing those features to hit a goal for the path. Eg. moving 100 files in finder should not take more than x ms
The upgrade from Leopard to Snow Leopard on a plastic MacBook just made everything better. Things were faster, smoother, and you could run more things at the same time without killing the machine. It was the perfect OS. Then when Lion came around, it was the exact opposite, it felt terribly buggy, and made everything clunky and worse. At least that's my memory of these OS updates.
Makes me wonder whether this alternate major release cycle was a good idea. If you delay all feature development for a year, you'll get a barrage of features once the performance-only OS version is out the door, and there's not enough time to do all of them properly, so you get buggy and slow versions.
Maybe doing performance improvements and feature development at the same time would have been the better choice? How is it being done at Apple nowadays?
