Ok found the problem.
I had removed all references to aircrafts on AAI's side (which was made very confusing by those changes being made twice in different files in the mod, (in prototypes/ai-vehicles.lua and in prototypes/entity/entity-update-eternals) in case someone trying to do the same wonders why it's not working) given i have those disabled in it's config as they're not compatible with the realistic aircraft patch and it still failed to load despite the weapon loadouts being back to normal.
Turns out in data-final-fixes.lua lines 88-96 you assume that if AAI Programmable Vehcles and Aircraft are loaded then the AI aircraft versions are in, which they aren't if they are disabled in config.
It's the AAI prototype names that led me to assume it was referencing the weapons when it really wasn't.
Deleting the offending lines fixed it for now, but a check that the aircraft actually exist should be added.
