The Washington Post's Geoffrey A. Fowler posted an interesting article in which he details how new smartphones are under-performing older ones in terms of battery life. Geoffrey puts 12 smartphones to the same test, and checks which ones dies first.
It is interesting that the new 2018 smartphones under performs similar smartphones released in 2017. Geoffrey's conclusion is that new display technology - high resolution OLEDs, are the culprit. The main reasoning behind that is that the iPhone XR (with its LCD display) performs better than the iPhone XS, even though the XR has a smaller display.
But as you can see from the test image above, the phones are used to show an almost completely white and blue screen. When showing such images, an OLED display will indeed draw more power than an equivalent LCD... but this is not normal use, and in most applications, images and videos, an OLED will be more efficient than an LCD.