More annoying than performance is the ever increasing nagging for apple paid services, apple pay, apple icloud, etc. The platform is literally becoming a junk adware platform. It feels like an infected PC that pop ups ads randomly.
My main problem is that if I simply want to do something on any iOS now as soon as I unlock it I'm blocked by pop ups for things like making a back up and buying more iCloud storage and upgrading to iOS 11 -- things I never intend to do. There's no way to switch these off either. And they happen constantly, multiple times a day.
Last time I used my iPad I dismissed a popup, opened up an app and the same pop up came a few minutes later completely interrupting me. I have no tolerance for these annoyances.
Samsung phones were complete trash back in the day with their bloated interface but I've since switched to a Note 8 and the experience has been very good. UI is very clean and the performance/features on the phone are outstanding.
The iPhone is a rather one size fits most device. If you don't want to go along with Apple's idea of how to use the device, you will be unhappy with it.
Right now I'm fighting the practically forced upgrading of a particular app for which the update will remove functionality. But in order to not update one app, I'm forced to manually update every other app individually. Which is about 40-50 updates a week that I have to approve.
Using the phone forces me to realize the extent to which I don't really own it. I'm just sort of renting services from it with an all-or-nothing set of features.