My explanation of the analogy was imprecise. I'll rephrase.

"Stagecoach" elevated the western genre out of the catagory of "B" movie to critical heights previously unheard of for that genre.

"The Dark Knight" did the same thing, insofar as it elevated the comic book movie out of the catagory of "popcorn" flick into critical heights previously unheard of for that genre.