Alright, with my experience with a flagship phone I would like to make a few observations.
I have only plugged a cable into the USB C port twice throughout me owning it. I pretty much exclusively use wireless charging. I transfer through FTP, so I don't even plug it in to transfer files.
So I more or less have an unused port, so my opinion of removing the headphone jack has changed. I don't mind it as much, I would still like 2 USB C ports as a replacement for the times that I'm on the road and need to use a battery bank, or for USB OTG purposes while still listening to music, but a quarter inch headphone dongle isn't the end of the world with wireless charging and the extra features that modern flagship phones have.
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Obviously the next step is no ports at all. People joked (in a "actually this isn't a joke we know it's coming but it's a joke because it's so stupid" sort of way) that was coming when the headphone jack was removed and it looks like we're close since some devices were even announced already.
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@DrMacintosh None, because batteries deteriorate over time and any OS or application becomes more hardware-intensive as more features are added, even in Apple's case.
Yes, iPhones' practical longevity is the best on the market HANDS DOWN, but no iPhone from 2015 is "good as new." Hell, my iPhone SE from late 2016 is not what it used to be.