My iPad Air 2 still works and opens websites, especially MR. Content blockers work too, YouTube in Safari works. It is a bit slow because it got 2GB RAM but even Instagram works. It doesn’t hold battery for long but can still be used. I believe newer iPads are much better, especially versions with more RAM
I have an iPad Air 5 on iPadOS 15 and it’s still compatible.
As far as I know, the issue with that “middle tier” in terms of age of iPads is battery life when updated.
The devices are good, but battery life has suffered too much if fully updated, they did not age well in that regard. Newer iPads that were significantly updated have fared far better.
By the middle tier I mean A7 through A12 (or A11) iPads. The iPad Air 1 to the Air 3, 1st and 2nd-gen Pros primarily, 5th through 8th-gen regular iPads, etc. The early 64-bit iPads’ battery life has been absolutely massacred by iOS updates. It’s sad, because their usability has dropped far more than the iterations that followed. The same thing has happened with iPhones. iPhones like the 6s work well when updated, but battery life is garbage. I know that because I have an iPhone and an iPad from that time that were forced out of their original versions by Apple.
Performance is very usable, no crashes, no problems apart from a slight slowdown and occasional keyboard lag. If fully updated, battery life barely breaks the 3, 4-hour mark. A massive drop compared to the easy 12+ hours they get on original versions.
If only battery life were slightly better, their late-life usability would skyrocket. My 9.7-inch iPad Pro is on iOS 12 instead of 16 and the difference is massive, I got 14 hours on iOS 9 and I’m getting 10-11 on iOS 12. 9.7-inch iPad Pros on iPadOS 16 as used and as old as mine would be lucky to scrape 5 hours if updated. Massive difference.