Are you sure about this? Maybe with heavy use this is true, but my Air 5 is by far the best iOS device ever in terms of battery life. Web browsing, TV shows, reading, low brightness, and I get like 25 hours of screen-on time.
Neither the 9.7-inch iPad Pro nor the iPad 6th gen on their original iOS versions are anywhere close to that, both standing at about 14 hours (I tested the iPad 6th gen and I was shocked to see that it was similar to the 9.7-inch iPad Pro when it was on iOS 9 (it was pathetically forced to iOS 12 by Apple and battery life plummeted), but maybe I should test it again sometime, that said, every partial test I’ve run indicates it is at 16 hours at most, not a lot better), so if I had to guess, I doubt the iPad 9th gen gets anywhere near 25 hours. Maybe the M1 is too efficient for these tasks and you’re taking heavy use into account which presumably shatters battery life? Because like I said, even large-battery, efficient iPads on earlier - and more efficient - iOS versions aren’t anywhere near the Air 5.
For reference, I got 9 hours of screen-on time from 100% to 63%. Like I said, I doubt the 9th gen can be better than that.