And you have to remember, it's not JUST screen time that uses battery power.
A significant amount of power is used on the Cellular connection (as well as WIFI, Bluetooth, GPS, Audio, Processor speed, etc.), among other power hogs. And since signal levels dictate the amount of power required to maintain that connection to the tower or WIFI access point it's unrealistic to simply compare screen times and use that to gauge battery usage overall.
In fact, it's extremely difficult to do an Oranges to Oranges comparison of two phones for battery performance and have only the screen time be the determining factor. The only way to even come close to successfully doing that is to take 2 phones with the exact same configuration (apps installed, accounts set up, screen brightness set to static levels - since varying room brightness will vary screen power consumption, etc.), and run the same movie or website on both while side by side in the same Cell Site and/or WIFI connection.
In other words, the differences you see could easily be the result of any number of other variables you've not given consideration to.
