Yes the C5 is not a flagship device, it's a mid range one going by the specs so we can expect the Z5 to be greater than the Z3 now considering the C5 specs. I suppose what has happened is that rumours got muddied between C5 and Z5.
At least I hope so anyway...
On another note, I realise now how some people ghet insane screen on time with phones, last night I fell asleep browsing reddit and must have dozed while viewing a gif, I woke up with a warm phone but nothing major, and the gif looping in the viewer, screen on:
So this kind of points out that screen on time is somewhat meaningless given that phones will vary by huge amounts depending on what media or app is using the screen. In my instance an animated gif was looping and consumed just over 30% battery for 6 hours SoT.