eInk is like a piece of paper, which gets MORE visible in the sun, but standard touchscreen LCDs/OLEDs get harder to see. I am not sure about the physics/reasons for this. Phones also aggressively dim screens to conserve energy and lower temperatures. Phones absorb a lot of sunlight, so a white eInk display is brilliant in that regard.

Refresh rate is a solved problem for eInk as well, but it comes with energy tradeoffs and... might still be proprietary. But 60-120 fps eInk exists AFAIK.

Trying to outbright the sun on a battery-powered device is an approach I've always found questionable.

E-ink, instead just lets the sun reflect off of it, does want some sort of light in the dark, but, perfectly visible in full-bright/direct sunlight.