Every iPad I've ever owned, including the Air 3, regularly exceeds Apple's stated 10 hours.
I was getting 16+ hours onscreen time with the iPad 4 though so the Air, Air 2 and Pro 9.7 were downgrades in comparison. Of course, performance on latter iPads was markedly improved over the iPad 4.
Plus even degraded standby time on iPad 4 is still very good. The Pro 9.7 meanwhile is seeing significantly faster drain on standby when battery goes below 50%. Granted, the Pro 9.7 saw very heavy use which likely contributed to the battery's quicker demise. The iPad 4 was always alternating with another device (iPad 3 followed by OG iPad Air) so at worst, it only had half the battery wear.
The basic A9/A10 iPads and I guess now the Air 3 are the only ones I know of that match or exceed iPad 4 battery life. Phone chipset + large battery makes for a very good combo in that regard.
If I could do a BTO iPad, I would choose:
iPad Air 3 body (with TouchID and laminated display)
Apple A12
6+GB RAM
1TB storage
USB-C
quad speakers
LED flash