There is no such thing as a "arrow machine gun", what Adam and Jamie made was a ballista (with the wrong ammunition) and there's no suggestion that Dionysus the Elder invented it. He invented a catapult.
Crossbows fire bolts not arrows.
Brady Ellison's archery skills are in no way comparable to a medieval archer.
Modern bows are far more powerful, and he failed to match actual archers in either speed or accuracy.
11 shots in 2 minutes is just under half the speed of a trained archer and (as stated in the Splitting an Arrow) medieval archers could hit the shaft of an arrow, while Ellison couldn't hit a person.