Yeah but MBP aren't running 4k. 3k/2560p screens seem to have a lot easier time with battery life at the moment. I actually think Apple is being more sensible than say, Samsung when it comes to the resolutions they choose.

I looked at reviews of several laptops with a 1080 vs a 1440 vs a 4k option and 1440 > 4k was the biggest drop in battery life.