To say that football today is played the way it is as a result of Don Coryell’s innovation would be like saying we wouldn’t have airplanes without the Wright brothers.
Someone else probably would have figured out how to angle wings and develop a movable rudder for a heavier than air plane – just like some football coach would eventually have put a tight end in motion and lined him up in the slot, forcing opposing defenses to play an extra defensive back and thereby essentially creating the nickel defense, too.
But it was Coryell who did that.