These are mini-LED displays, so way more LEDs, plus hardware/firmware to constantly light/dim these lights as needed. Regular LED screens just turn on the backlight and that’s it, unless you change overall brightness in settings.This is far from a controlled test, but when I use iStats pro to check my 2015 MBP 15 inch while viewing MacRumors, at 8 clicks of brightness I idle at around 12 watts, and at full brightness I idle around 19 watts. So based on that, I think display brightness does make a big difference.