I hope it's inaccurate, because if it isn't, then iOS 11 and 12 absolutely destroyed the battery life of a friend's iPhone 7. I knew battery life had decreased with iOS 11 (he was getting 5-6 hours on iOS 11... I'm getting 8-9 with my 6s on iOS 9).
I checked my friend's battery life on iOS 12, and it was - according to a manual add-up of Screen Time - 2.5 hours of use (both on and off screen, equal to the pre-iOS 12 stat), with 25% battery life left. I hope that isn't correct because it would mean that iOS 12 is far worse than iOS 11 in the battery life department, and iOS 11 was bad enough already.