I think you make a lot of good points here. I’m curious if carrying around spare batteries is markedly more convenient than having an external battery to plug into. It doesn’t seem to save money, especially if you have more than one spare battery. Also, do those extra batteries have to be charged in the phone, or can you plug them into a charging cradle so your phone is available for use? Both of those options seem somewhat inconvenient. Also, don’t swappable batteries compromise waterproofing? Like seemingly everything in tech, it seems like an issue of tradeoffs, and I would never criticize someone for choosing whichever tradeoff works best for them and the features they prioritize. But I’m guessing that phone makers have realized that most consumers don’t prioritize swappable batteries and probably don’t own them, and decided that having swappable batteries wasn’t worth the compromises, especially since it clearly hasn’t hurt Apple at all. In that sense, function hasn’t been affected by losing swappable batteries.
Re: the headphone jack, I’d say that I have better than average hearing, but apparently not enough that Bluetooth sound is unlistenable compared to wired. And I love being able to just set my phone down and walk all over my kitchen or yard without a cord. So for me, Bluetooth has improved function.