Consider the Ericsson MC218 / Psion Series 5 (https://www.google.com/search?q=psion+series+5). The software (EPOC, forerunner to Symbian) could drag windows (whole windows) around the little screen faster than the LCD crystals could keep up/redraw.
I had a look inside the unit (find the photos at https://www.applefritter.com/content/pocketable-ultra-low-po...) and found only a 36MHz ARM7TDMI inside. Presumably the CPU was doing the window redrawing all in software.
It's really reassuring to me that such a slow CPU gave the LCD a run fo its money, because let's face it, doing $tons_of_pixel_manipulations on a CPU always chews power, so if you want battery life you're going to need something that works well at the low-power end of the spectrum. (The Series 5's monochrome LCD was 640x240.)
So, well-designed software would meet the power consumption-versus-feature challenge halfway. Such software doesn't exist yet though, and it appears this status quo isn't going to change anytime soon; the (financial) investment required just doesn't seem to be materializing.
I'd say the main problem is market effects, and consumer interest. "Yeah 70% of CPU time goes to drawing the screen" is NOT particularly attractive.