They've kind of established the A-wing as the Rebels' mainstay fighter in "Rebels," which actually makes a certain amount of sense. It's small, portable, easy to build, and fast as hell; all of these are characteristics you'd want in a fighter used by a guerilla force that prefers to avoid direct engagement.
Not exactly. All we know is that the A-Wing was used by one, possibly two rebel cells sponsored by Bail prior to the formation on the Alliance. We have no information on what kind of starfighters any of the other groups were using (if anything.) For all we know Dodanna's cell has been using X-Wings right from the get-go and we just haven't seen them yet. I doubt it, but it's not impossible.
Ugh. I hate the West End backstory for the X-Wings.
But I thought that was re-canonized BECAUSE of the U-Wing? The U-Wings were just barely getting made when the Incom team defected?
For the sake of clarity, here's pretty much the sum total of relevant canon information on the subject from the 'Rogue One Ultimate Guide' book.
The one on the left is obviously from the U-Wing page, while the one on the right is in reference to the X-wing. The full story of Incom hasn't been told yet so we don't know when Incom was nationalised or exactly when the X-Wing designs were shelved, nor indeed when the rebels acquired them.
All we know is that as per the 'Ahsoka' novel, some model of TIE was already in Imperial service as early as 1 year after RotS, so it seems likely that Sienar had already won out by then. There's also no reason to conflate the two instances as they could have occurred years or even decades apart.
Either way there's no mention here of direct collusion or defections, just that Bail managed to get his hands of a shipment of gunships though nefarious means.
I'm assuming the bit about the civilian version being less scarce is mostly just a bit of foresight on the part of Pablo, on the off chance someone else wants to use the design in the future or some VFX artist sticks one in the background of some shot.
Between West End and the prequels not showing any X-wings, the original 1977 backstory went out the window. At least we have Y-wings.
I think it would have been a bit weird to have X-Wings to show up in the prequels given how iconic they are in relation to the OT. From a thematic perspective it wouldn't make sense either since Lucas was showing a period of cultural transition from the bespoke, craftsman like engineering designs like the N-1 and the J-327 and the more industrialised, utilitarian mass produced designs of the Empire.
The only place they really could have showed up was in RotS and that's where we got the ARC-170s, which are clearly meant to be a definite nod in that direction, but evoking more of a WWII type of aesthetic.
P.S. You know having said all that, *technically* a single X-Wing does actually appear in AotC...
