Ooh! Something more to think about!

I think it likely that you are right about the writers giving him skill only when the plot requires it -- I'm hoping that whole statement can move into past tense any day now -- but I'd prefer explanations that are coherent with the universe. For example, different weapons handle differently -- IRL, being a good shot with a rifle doesn't necessarily map to being a good shot with a handgun, which may not map to being a good shot with a crossbow, which often doesn't map to being a good shot with a compound bow. OTOH, it does feel just a little ad hoc to shrug away the incident you cited with "it's a different weapon."