Since kit Kat update, my s4 began doing the same, I've always monitored very close the battery stats and screen was always way up with about 60% of the battery usage, but like I said I noticed the change the immediately after updating to kit Kat, and my battery was no longer lasting my usual 4 hours of screen time.
Now, it seems that right out of the box, the s5 is doing the same, I'm getting almost 5 hours of screen time since I got it last week, with wifi and Bluetooth turn on all day for my Gear2, so I can say that this is giving me a huge increase of screen on time compared to the s4, so will be great to see what could happens if screen will come back to be the number one on that list, applying the logic above related to the s4, it should increase about an hour more of screen time.
The question should be, are all the other device with kit Kat experiencing the same? What could have changed from Jelly Bean to Kit Kat that is causing this increase on Android system and Android OS?