Is there actual evidence to back this up¿? I have used endeavour OS, openSuse and fedora silverblue/kinoite with gnome and kde when I was distrohopping recently and I found that battery life is the same irrespective of DE. Fedora and endeavour last between 5:30 and 6 hours while openSuSe lasted around 5 hours irrespective of whether I was using kde or gnome