> If we do that we might as well use a lightning to 3.5 jack-adapter

You mean a lightning to 3.5 and an usb-c to 3.5 one. With mandatory Apple/USB tax, DRM may or may not be included, and questionable DAC quality.

A fully passive 2.5→3.5 adapter is much easier, would work with all vendors, and has no potential DRM backdoor capability.

And we'd probably quickly see headphones with native 2.5mm plug and an included 3.5mm adapter, just like we currently have for "high-end" (read: $100) headsets and 6.35mm.

It solves it for the thinness problem. Which is stupid imo, cause why not just shove more battery in that millimeter (I thought the RAZR Maxx was gonna be revolutionary, no one cared apparently), but whatever. 2.5->3.5mm adapters are small and cheap...

Well, I for one do not care enough about battery life to pay the huge bonus the Maxx was selling for when I last brought a Motorolla phone (what I have no plans of doing again).

I'd pay for more battery life, but the bonus was just not worth it. It was easily twice as expensive as the phone I brought, with similar specs. Batteries last for a couple of days already, some more days are just not that big a differential.