I never had the fourth gen iPad or the Air 1, but I didn't like how hollow the iPad Air felt and the fourth gen was just as big and heavy as the third.
But going off of what I know about them, I'd say Air 2 > Air > iPad 2 > iPad > 4 > 3.
I only consider the original iPad over the 3 and 4 because it was the first and I was still pretty blown away by it.
What does that have to do with him not upgrading from his Air 2? Lol
He has the current iPad Air, which is the iPad Air 2, right now and he barely uses it, so there's no point in him upgrading to the iPad Air 3. He'll barely use that, too.