KDR of a single person means little yes, but of ALL time played on it? I think that means a significant ammount. Yes deathfire playing vagabond would suck, however again, all time stats means more then one person. To pad a race with 4600 hours is highly unlikely

Rapescallions stats- http://www.ibisgaming.com/wcs_stats/player.php?id=17387
Vagabond stats - http://www.ibisgaming.com/wcs_stats/player.php?id=17387
Flame pred stats -http://www.ibisgaming.com/wcs_stats/player.php?id=11888

A flem pred can escape after not procing anything with its speed(the same), health, and invisibility (your argument that the visibility is different for different players is null here, some invis> opaque)
A flame pred has 40% chance to drop their weapon and a 35% chance to set them on fire. Both will keep the flame pred alive if the guy they are trying to knife has not yet droped, giving the flame pred the ability to either run or get another go at it. If the flame pred fails he blows up hugging the guy he was trying to kill.

Rapscallion has 22% chance to crit, if he fails to crit he is dead, running away is difficult, very difficult, they can see you and they dont have anything blocking their vision, slowing them down, or preventing them from shooting like a flame pred would. Their ultimate is useless as all it does is bring attention to their self, makes too much noise and is visible through walls.