It's kills, not takedowns, so your 17-0 doesn't necessarily mean anything. Takedowns includes kill assists, and this order is looking for killing blows.
I agree that it's a bit much, particularly in PvP mode. You can do 90% of the damage to an enemy and lose the kill to a teammate who gets the final blow. I agree with Gammony, either making the order be takedowns instead of kills, or lower the streak needed (get 2 kill streaks of 5 or more in skirmish matches instead of 1 of 8 would be better IMO).