Exactly this. About 7 years ago I bought a secondhand Alphasmart and started using it. I loved it for what it was but I had to stop using it because I could not see enough of what I had written.
I’m now using a Pi with a monitor in portrait mode and FocusWriter to write. It is a fantastic single purpose writing device. But I would pay money for something similar with reasonable screen real estate I could stick in a bag.