That's another of the reason i never like legends. People that write these stories leap on every detail of 3 2 hour fils and desperately try and work their own thing in.
3 seperate stories about what happened on Ord Mandel or whatever.
The idea about B wings and A wings being created after ANH is purely cos they didn't appear in that film? So they think it's a cool idea to write about how they were made, but there's juts no reason to assume that they didn't exist just because they never used them in the single rebels in space scene in the whole film.
Sure, let's not use the things that can get it done better.
Who needs those stupid, fast Ceptors, let's just swarm it all! Who needs those dumb B-wings, let's use the rusty-old Y-wings!
There's only one B-Wing, and it's a prototype. They'd prefer a fleet of Ys for sure.
I get people need reasons to hate rebels, but lets cool our jets a little shall we?





