I think everything to say about this already has been said, but I’ll put in my two cents anyway.

We see Stormtroopers successfully defeat their enemies on the Tantive IV and on Hoth. Obviously there’s also a lot of plot armor regarding the main heroes always escaping and as we see on Endor with the Ewoks, who I’d also argue were pretty good warriors in their own rights.

They really aren’t that bad of shots and I don’t think its unbelievable at all that Stormtroopers would have such good aim.

This is a case of a joke in the fandom becoming a genuine talking point and criticism I think, one based on little, or very circumstantial evidence, that then seems to become a predominant idea which is held as almighty truth by some because it is reinforced by memes and jokes. (Again, my two cents on this.)