yes, they exist. But it's due to the fact that certain areas of the map can be defended against common infected very easily, only thing to kill is the tank. And when that happens, even the biggest idiot can aim at a target which is on it's own. Sigh.
So now you get REAL records like mine at 12 mins, only to be beat by some exploiting nab with 18 mins.
Besides the leaderboard is based on your friends only list, so you can tell if someone succumbed to the evils of exploits. Because remember they let you do it! so it's not cheating(!).
side note, gotta laugh when people run to the corner camp/closet spots and find theyre not there roflol.