Of course THE AVENGERS appears to the lowest common denominator. Because it's fun, and because it's a great concept.
But, while it was a better written film, THE DARK KNIGHT was a film that ALSO appealed to the lowest common denominator. Because it was fun, and a great concept.
Someday, some "brilliant" director will figure out that there's a happy medium and make the best superhero movies ever.
I see nothing to suggest that the fighting has improved in TDKR, not that its been that bad anyway. Batman is using the same types of moves he's had for two movies. He's just doing it in a crowd full of people now.