I dont think rebels and clone wars should be cannon.
I meam b wings can one shot an ISD? They are flying both b wings and a wings before ANH when it was shown that a wings didny come around till ESB and bwings showed up around ROTJ
And an A-Wing took out an SSD by running into it in RotJ.
Legends fluff was that those craft were not around. Current fluff is they were, they were just not at Yavin and Hoth, just like Tie Bombers (which we know were around and yet are not seen).
Real life reason none of those ships were in the original movies was budget constraints though.