I love composite bows for a reason. The ease of use, firepower, and accuracy of shot are unparalleled. That alone is not why the Mongols conquered such a large territory, but it is a solid part of it. Of course, he was shooting a still target. Archers behind shields would have a bit better of a shot retaliating. Also, heavily armored cavalry can disrupt that a bit (in Civ5 terms, use Knights to counter-attack, since Keshiks have about the same strength as paper).
But 12 shots in less than a minute is damn impressive.