I wonder at what point you put in a flight control computer. I could imagine with a plane that size it's easy to put some big forces on it with heavy inputs.
ELRS (radio), Ardupilot (Flight Controller), EdgeTX (Radio OS), and Mission Control (Ground Station SW) are serious tools used by many in the hobby. Them being open means there's a lot of competition and a lot of features. But also not amazing UX :)
[1] https://ardupilot.org/ [2] https://inavflight.github.io/
This sounds exactly like the sort of business I would want to build :D