"But many users have setups with studio monitors, amps, and other pro audio gear that do not have wireless solutions and need the 3.5mm jack."
Any user with "studio monitors, amps, and other pro audio gear" is not using the 3.5mm jack. I dabble in music production (i.e. I'm very much a beginner) and I use an USB audio interface. The built-in DAC, while better than most PC's, is not very good.
How does Schiller even pretend that this is a valid justification for the 3.5mm audio jack on the Mac but not on the iPhone?