> It takes more power for your phone to drive headphones than it does to transmit a bluetooth signal.

...are you sure? And, is that still true even once you consider the extra encoding the phone’s CPU has to do?

I was under the impression that conventional 3.55mm jacks output exceedingly little power...

As someone who falls more in the "wired4life" category, the power draw of headphones has never been an issue, Even back in the naughts. That place of honor is reserved for websites, apps, and cell radios.

Ironically, with the loss of the 2.5mm jack power has a greater chance to be an issue, since your headphones and power have to occupy the same jack.