RJ,
Just watched the beginning of Hitman, forgot I had burned it. Things of note:
1) It is stated that the assassins are trained from birth to be "experts in every aspect of combat" and that Agent 47 is "the very best of them."
2) I also watched the sniper scene, there is no way to tell how far exactly the shot was in the screen, he's far far away and the camera moves to quickly to judge. Stands to reason that the camera speeding up is to compensate for the long (over 4km) distance.
3) Most importantly, they know exactly where the shot came from, since 47 blew up the gun and case after the shot and the point of explosion was seen by many. So the stating of 4km stands as fact in regards to the movie, they weren't making wild guesses.
4) "It's in the movie so it counts", as you say.
So stop acting like a child and just deal with the fact the the fictional Agent 47 is a far superior sniper to the fictional Swagger, ergo, 47 wins.