Hardware might be related to software. The swiping from screen to screen was slow. I posted about this and people said to turn off animations. Annoyingly this was not straightforward and it didn't solve the problem. Not to mention having a unique charger meant an extra device to pack on trips.
The os annoyance was the relentless "type in your apple id password", and multiple times per week updates. A few users have spun the narrative that updates are good, but these were annoying and didn't have any front facing benefits. No widgets really sucked, it was regressive not to have my next alarm time on my home screen.
Finally Apple maps sucked, the podcast app was buggy, I'd hit play and nothing would happen. I'd then hit play a few times and nothing would happen. Then finally something would happen. I can't remember other software bugs, it's been years.
Sure these might be fixed today, but I wonder what other things are bad today. I have ad blocking and a few other non play store apps on my phone, given the App Store, I'm not sure Apple would let such apps through.