Never being hurt in battles involving thousands of people, most of which were trying to kill him and his allies. It takes quite a bit of skill to do that. Especially considering how he wore no armor. Not to mention the cave troll swinging the chain. He dodged it a couple times.
Barton won't be dodging the 10 arrows flying at him. Legolas was speed shooting on that shield. Not quite as fast as normal, but still faster. Still kill shots.
Well, its too bad that neither of us can find a clip. I know the scene you are talking about, I would just prefer to watch it again.
And the Chitauri had to fly in a straight line. If they had been zig-zagging then I would say he is better. Not every Uruk was moving towards him. Many were moving at angles. He still got them.
Legolas had no need to move before, while, or after shooting. Everything was dead by then. The one time he did, he still killed everything. Though he has shown one-shot kills from horseback, from the back of a charging Mumakil, and from ontop a shield, going on to launch the shield into an Uruks neck. Amon Hen he snap shot a couple right after sprinting (which would be hard as hell, considering how he was hopping to slow down)
He fired what looked like 10 yards into a 1 inch hole in a door (partially covered by splinters) and killed a goblin. He was shooting multiple moving goblins in Moria from at least 100 yards (vertical distance as well) and the goblins are maybe 3 feet tall. One shot kills.
The carrier shot required hitting a massive turbine, and Barton took far longer to shoot than Legolas ever has. While there was some insane adjusting and all, I have faith Legolas could do it, given Barton's bow and the same circumstances. For that kind of stuff, experience is what matters.