Standby time has worsened with newer iOS versions, inherently (i.e., regardless of updates). My Air 5 has significantly worse standby time on iPadOS 15 (original iOS version) than my 9.7-inch iPad Pro on iOS 12 (forcibly updated through three major versions). iPhones exhibit similar symptoms starting with iOS 12.
The iPad 4 was great, but only two hours ahead of the two future 9.7-inch iPads on original iOS versions I’ve tested (16 vs 14 hours, 9.7-inch iPad Pro and 6th-gen iPad). The Air 5 is ridiculous on iPadOS 15 with light use, getting north of 25 hours.
Yeah, that’s the thing about running old iOS versions. If enough time passes by, compatibility is too compromised for it to be useful. I have an iPhone 6s on iOS 10 and it’s not useful for web browsing, and app compatibility has been significantly curtailed. Sadly, there is a limit, a point in which older iOS versions (and older iPads by extension) are old enough, even when not updated.
I doubt a 32-bit iPad can do much today (and they get to iOS 10), and that applies to newer iPads left behind.
An iPad Air 1 on iOS 7 is great... but for what? It can basically use Netflix and not much else.
Sure, there’s a specific subset of things that will work, mostly content-consumption oriented (iBooks, Netflix, Music, etc), but if you want to use it for a bit more than that, you can’t. Even some games from back then have been removed from the App Store.
It’s a little sad to think that there will be a point in which all iPads derived from Apple’s original design idea (the 9.7-inch design) will be obsolete. Even the current state isn’t great, with the alternative being awful too. Update them and they result in an awful experience. Sadly, this has been the case for all 9.7-inch iPads.
The 4 32-bit iPads are gone when updated, they work too horribly. Air 1 and Air 2? Not great. 9.7-inch iPad Pro and 6th-gen iPad? A little better, but still bad, and like
@Digitalguy said, nowhere close in terms of performance to the 10.5-inch iPad Pro.