If you don’t track it, it is very likely that the difference was significant. It has to be very noticeable, otherwise you wouldn’t notice at all, I think. This isn’t your case, obviously, but I say that based on the hundreds of conversations I’ve had with iOS updates-cause-battery-issues deniers. I’ve always said - and given very precise statistics to support my claim - that iOS updates obliterate battery life, always. I’ve repeatedly asked people who deny this the following: “okay, battery life is the exact same as it was on original iOS versions. Give me numbers, give me screenshots”. Invariably the answer is “I don’t know, I’m not obsessed, I don’t follow it”. Yet they deny it. I digress a little, it’s just to show that if you noticed and don’t track it, the difference was likely very significant, like I said.I don't have hard numbers on the screen time. It was a general impression the 10.5 isn't holding its charge like before. It certainly wasn't 10 hours, but then I wasn't using it for hours on end. Sometimes I'd use it for a few minutes and other times for a couple of hours.
I have an iPhone 8+ which I am quite happy with.
15.7 on my Air seems a bit different than 15.7 on my old Pro. It's as if some menu options have moved around a bit and maybe if there are added options I don't recall being there before. It's weird because I can't identify exactly (from memory) whats different, but it does seem slightly different.
The iPhone 8+ is the pinnacle of not-full-screen iPhones. I’ve never had one, I’d love to. One of my favourite iPhones I haven’t had.
Unfortunately, I can’t help you with your last point. I have a 9.7-inch iPad Pro, but it is - and will remain - on iOS 12.
Thanks for the answer!