The Aurebesh letter for X does not resemble the english letter at all. Therefore, the retcon for Aurebesh’s existence in place of the English in ANH means that there should be no way anyone could’ve known to name a ship an X-Wing.
Except that they apparently have kept the English lettering (I don’t think that’s the correct term for it, though) in the canon as a sort of “fancy” script, i.e. the galactic equivalent to cursive handwriting.
I don’t think the retcon was necessary either but *shrug*. They did it anyway and we have to live with it now.