Rofl, Joker, _TPs don't talk of killstealing.
Sometimes you poke one, and he's dead, sometimes you poke and he's interrupted and the ally kills him.
That's the way it is, you are right.
I feel it's a bit... well... unfair. The guys in front of you risk their skin fighting the enemy, while I stay back in safety, but however have the same chance of killing him.
On the other hand I am pretty screwed in 1 on 1 against any more or less capable fighter if only using a spear/pike. But as I can always switch to another weapon, and I do so, this is no excuse for me.
So please forgive me if I have a bad feeling when killing people from the second row. On the other hand I would also have a bad feeling if I decided to not participate, because if my teammate gets killed then I would have a bad conscience, too. Difficult.