Sry, I did not say I were using the iPad in the SAME way - I said "very similar" and described it.
The average and most frequent value is 11:50 before / 10:00 after the update. Too hard to understand for you?
For the winter period, when the update occurred, brightness could be similar because a) I almost always used the device at the same place with the same environmental light conditions, b) for similar periods of day / night conditions and c) I always adjust the brightness as closely as possible to a pleasant level, which I can do consistently because my lighting perception is consistent.
For the summer half of a year, I also was outdoors. If so exclusively, I consistently got ca. 5 hours after the update. If mixed indoors / outdoors, then in between these 5 and the 10 hours of pure indoor use. During the following two winters with again pure indoor use, it again was the 10 hours. Sorry for not having mentioned summer experience before.
I know that it was not battery wear because that started noticably only later after 3 or 3 1/2 years when it fell slowly and continuously from the 10h indoors or 5h outdoors to first slightly, then somewhat lower values.
Why do you ride so much on battery capacity and external wattage measurements? What matters for the enduser is his actually experienced battery duration.
Millions of other reasons, LOL. Why not trillions. One of that many different bugs iOS might have got to affect battery life from the day of the iOS update on. It is not that I was "holding it wrong" from exactly that day on, or maybe Steve Jobs would disagree;)