720p is pretty solid on small screens when you're holding it ~2-3ft away. 1080p would be more ideal for sure, but I wouldn't be that disappointed if it means better battery and performance.
Yeah that sucks but if it’s a brighter high nits LCD screen than i might prefer that more on a portable device than the deep blacks of OLED. I use my OLED tv when I play at home anyway.
It is very hard to get low resolution small oled screens. Cell phones use pentile displays that are about 60% the actual RGB resolution of the input they need. You would be looking at it needing to be outputting in the 4k range on a 1440p ish display to use off the shelf parts.
If you wqnted to have a 1080p RGB oled it would need to be about 11" and that is too big. It would also have burn in issues with any reasonable brightness.