uh...think you might be getting a bit too excited about barrel-roll there
first of all, no way in hell is Vector Thrusters worth even close to auto-thrusters. If autos cancel even 1 damage, they're a complete steal. There is no real choice there, you either take no modification or thrusters. If you're desperate to roll, you take Jake Farrel and thrusters.
similarly, there's no reason to put it on either X-wing. Giving up Integrated and adding 2 points to something that fragile and inefficient? Why? W e have bb-8!
no no, Vector Thrusters is only going on one kind of pilot: **** good abilities flying wet cement with engines somehow stapled to it
namely Palob/Mux, Norra (if opting for a non-bb8 build), and maybe Miranda.
VTs will not make inefficient/kinda bad pilots like Cobra any better; just more expensive
I disagree on vectored thrusters vs autothrusters being open and shut. If a barrel roll moves you out of arc and prevents you from being attacked, it's possibly saving you more than the 1 damage that autothrusters would save you, therefore also a complete steal.
BB-8 is great, but vectored thrusters opens up other possibilites. How about a T-65 plus vectored, PTL, and R2 Astro? It's got a much greater range of movement and the ability to go both focus and TL if it doesn't need to reposition.
it's very open and shut
if barrel-roll would move you out of arc, you're probably already playing Jake farrel as none of the other commonly seen A-wing pilots (re: the generics) are of high enough PS to effectively arc-dodge
as for the t-65 with vector PTL and r2 astro, it's essentially a really really crappy interceptor and an extraordinarily crappy Vader.
neither the X nor the A are arc-dodgers (except Jake); VT won't magically turn them into ones either. They're still going to miss crucial action efficiency that propels the likes of Vader/Inquistor/Soontir/Whisper etc etc etc to the heights that they can reach