I agree with you that the 6+/6s+ probably have a better battery life overall, but your cellular signal seems to be really poor in your screenshot, and it doesn't help the battery life at all.
the poor signal occurs only after 6pm when i get back from work. im on wifi during those times but aware signal will be present still. battery life is getting better after disabling icloud for now. been on lte most of the day listening to music and some youtube and struggling to get it to 10%
usage is over 10 hours now