Yes I have seen posts about and users claim it. But I have never seen hard numbers to prove it. I searched for articles or videos in which they perform from battery tests with kde and gnome but I found absolutely nothing. I actually measured it when I was distrohopping and found no difference so I see no reason to believe those people when I have my numbers.
it looks like it HAS improved, hence my Ubuntu comment. I believe Wayland has something to do with it, too, since it scales hi res screens better than xorg
Maybe this is true. All my testing was recent because I had a new laptop and was figuring out what I wanted to install on it. Wayland version of both kde and gnome were what I use. Also I remember fractional scaling on gnome under x11 came with a warning of extra battery and CPU+GPU resource usage.