Something I missed in my previous comment that is quite common in sentiment is that just like some people keep their iOS devices until they don‘t work well enough for them anymore, I don’t feel particularly compelled to upgrade if my devices work well for me. I have high standards, which is why I don’t update iOS.
I was fine with my iPhone 6s and 9.7-inch iPad Pro on iOS 9 until, just after upgrading to the iPhone Xʀ (upgraded due to battery life, but it‘s not like I wasn’t happy with the 6s: I still use one on iOS 10, and it’s probably my favourite iPhone ever), my 9.7-inch iPad Pro was forced into iOS 12. Battery life plummeted, and even though performance was fine, there was some occasional keyboard lag that wasn’t there on iOS 9. Nothing major, totally usable, but like I said, I like it when they work properly. Apple set that standard, not me: iOS devices on their original versions are flawless. The 9.7-inch iPad Pro, therefore, wasn’t perfect anymore: battery was mediocre, performance was great but not as good as it used to be. Some months ago I upgraded to the Air 5, and now I’ve restored that: iPhone Xʀ on iOS 12, iPad Air 5 on iPadOS 15. Both perfect, both great, no complaints. Regardless of any launches, I’m fine with my iPhone: it does everything I want it to, the way I want it to. Is my current combination better in terms of features and functions than the first one (even though now both devices were forced out of iOS 9)? Yes. Would I be fine with those two devices on iOS 9? As long as they do what I want them to, also yes.
Like I showed with Apple’s forced update of my 9.7-inch iPad Pro, that great (obviously subjective) value immediately plummets if the device does not work like I want it to.
Later addition: I just realized that I wrote the 9.7-inch iPad Pro’s tale in the past tense, for some unbeknownst reason: I still have it and use it; it is still on iOS 12. I also made it seem like I don’t like the 9.7-inch iPad Pro anymore, which would be inaccurate: it’s my favourite iPad ever, even if it isn’t perfect in terms of battery life. I can tolerate a decrease now that I have another iPad, and even when I didn’t, it wasn’t that terrible. iPadOS 16’s reports hover around the 5-hour mark, and I’m getting more than twice that. Not perfect, but it’s half-decent. It still bothers me, but after seeing what iPadOS 16 did to the first gen Pros in terms of battery life, I have to be grateful I get 10-11 hours and not 5.
I like it because I consider it the best iteration of Apple’s original idea for the iPad. Apple could’ve evolved the 9.7-inch iPad in many ways; for once, they could’ve killed the design language before launching the iPad Pro, and they didn’t. Even if it isn’t the last 9.7-inch iPad (that goes for the iPad 6th gen), it is the best one: the best processor (A9X > A10, in many ways), the best screen, and the Pro features at the time, like True Tone, Quad Speakers, and the screen features like I said (this iPad being the only 9.7-inch iPad ever with those). Considering that there will most likely never be a better 9.7-inch iPad, it will probably retain that value forever: many would consider that device obsolete, especially when Apple discontinues iOS support, but for me it will always have that distinguishing feature. And because of that, and alluding to the thread’s question... I will never sell it.