SETP is used rarely to compute parity, though it doesn't really save anything if you can use POPCNT. PF is also used by floating point comparisons with a different meaning though that is not useful for the Arm extension from Apple.

AF indeed is basically unused. The problem for both is that you need them for accurate emulation "just in case".

You can eliminate flag generation almost all the time with a little optimization (slash deoptimizing if you hit an unexpected use) but it certainly is less convenient to have to implement an optimizer.

The unexpectedly hard bit is switch statements, which are the main case in which compiled code has two back to back jumps... therefore the input flags come from a different basic block and you don't know which instruction generated it.