I don’t disagree with you there. I reckon you’ll probably get a good level of performance on your iPhone 11 along with a 25-30% decease in battery life. If you end up with roughly 7-8 hours of SoT I reckon that’s acceptable given that all your apps will be compatible again. It’s a fair trade off. Modern iOS versions are less optimised on older phones, we are aware of this and, as a result, battery life takes a hit.The newer you go, the better performance is.
Battery life is the issue when you go too new.
I have, in the family, an iPhone 11 running iOS 14. For compatibility reasons, I will be updating and testing that one soon. We’ll see how it fares...
I expect performance to be good, because you’re right that newer devices suffer less. I expect battery life to be functionally obliterated. I can get the same battery life I get on the Xʀ on iOS 12 - 16 hours. Let’s see, with the same usage, how much iOS 18 gives me. I’ll copy the settings and the usage pattern.
I expect to get no more than 8 hours with very light use. If that’s the case, then battery life would be functionally garbage. But I’ll tell you later. From what you said, you consider the 11 new enough when it comes to updates, right?
Thankfully modern phones have larger batteries which, like iPads, make the battery life decrease much less noticeable as users still get a full day’s use out of their device before having to charge it again, unlike older pre-iPhone X devices.