Is that actually true? Five years ago it seemed like every phone had a QHD screen with some 4K options. Now most phones are 1080p, or are set to run at 1080p despite having higher resolution screens. The best phone display I've ever used was the 2560x1440 beauty on my Note 4 and I'd kill to get another phone with a QHD 16:9 OLED panel.
It seemed to be the last couple of times I was researching new phones. Though there is a significant caveat there that I don't buy top-of-the-range flagship devices as the hit when I break them is too high, perhaps the difference does not carry to the really fancy devices with all mod cons because they have more expensive but more efficient screens? The other caveat being that I'm going by 3rd party tests: this isn't something I've verified with my own study.
As mentioned above, overall tech could play a role in some larger and/or higher res screens doing better than they might compared to other models wrt battery life: IIRC Samsung use AMOLED screens which are generally more power efficient than the screens that might be used in my price range?
We also tend to use our phones a lot more than we used to, so they spend more time in a given day in active modes rather than standby ones, and many people have more background apps checking for updates than they used to, so there are extra short periods of CPU wake time, and radio activity, when the device would otherwise be in a lower power standby state.
SoCs being more powerful will have an effect too, but they are also getting more efficient especially when not in full use, so I doubt that this is significant compared to the factors I mentioned above.