I have noticed that screen on time calculation is fine differently in one UI 2.0 and it doesn't make sense and it is not useful. The primary use case of screen on time is to see the battery performace in a 0-100 charge cycle. That is more useful to me than screen on time in a day. I would be happy to see it come back.
On a similar note though, what kind of SOT are you guys seeing? I'm on the Indian S10 & I can't seem to cross 4:30-5 hours of SOT with one charge.