I don’t find that to be the case. In my usage I get around 14 hours from my Pro 9.7, which is the same as I got from my Air 2.
Arstechnica found it to be better in their review -
"Apple gives the same battery life figures for every one of its iPads, from the aging iPad Mini 2 to the top-end 12.9-inch iPad Pro: 10 hours of Wi-Fi Web browsing and nine hours of cellular Web browsing. In our battery tests, the 9.7-inch Pro nevertheless significantly outperforms the larger Pro and the iPad Air 2 (for reference, our tests are run with all screens set to 200 nits, and True Tone was disabled on the new iPad Pro).
The Pro and the iPad Air 2 have batteries that are roughly the same size: 27.5WHr in the Pro and 27.3WHr in the Air 2. I’m inclined to attribute the improvement to the A9X’s newer manufacturing process. The A9X is apparently built solely on TSMC’s 16nm process, while the A8X is built on a 20nm TSMC process. Our Web browsing test loads a series of pages in a loop until the tablet dies, and the WebGL test puts a moderate-but-constant load on the SoC—in both of these scenarios, the A9X appears to consume less power than the A8X before it."
I have noticed when upgrading iPads that restoring from a previous iCloud or iTunes backup can result in significantly worse battery life, but setting it up as a new device solves this problem.
The Air 2 is still a great device and I think it’s better value for money than the Pro 9.7. I only upgraded because I got a good price for my Air 2 and a decent discount on my Pro 9.7.