I know I'm late to this party but I just picked it up on sale and want to add that in Step One, you can actually kill most (if not all?) of the survivors in a level instead of delivering them. You'll get like half a star score but it'll let you play the next map, or more importantly; it'll let you play the same map using the Ostrich or Night Avenger. No need to waste time actually beating the mission properly if you just have to do it again right afterwards.
Also, there's just no way this game is a 7/10 for difficulty.