One point that as far as I can see has never been mentioned.
FD have never actually said why the race to Elite and other competions are in open only. The general assumption here is that it's because they acknowledge that open is the more difficult play mode.
However I think it's also highly possible it's really because they have more ability to monitor possible cheating in open mode. Solo mode is designed for minimal bandwidth. Open can use a lot more bandwidth and there is probably a lot more telemetry.
An excellent hypothesis +1
(Btw, I think I was the one who asked why there were few complaints about Race to Elite competition -- I am very curious about this)