Regarding the questions around when Diane was omegaed based on Field of Dreams, I think there are two main considerations.
Different dimensions don’t seem to necessarily be ‘in sync’ with each other timewise. In Rick’s crybaby backstory, he still seems to be fairly young when he spies on a Rick with a Summer and Morticia who appear to be around 17 and 14. My headcanon is that all dimensions were synced when the Central Finite Curve/Citadel was built. Therefore, if Diane was omegaed when our Beth was around 17, it could be possible that other Beths were older or younger and so experienced this at a different age - hence why sober Rick says Beth ‘was so little’.
Morty is making assumptions about sober Rick’s Diane. While she also would’ve been affected by the Omega Device, it’s possible that she did genuinely leave him and Beth years before she was erased.











