I kind of like it, since classes can heal them selves/one another either with skills or some good placement around A/C flag its not always clear who dealt more damage to someone and there for I like the idea of rewarding more than one player the kill.
Also need to remember the game plays somewhat like a MOBA, and killing/executing players and trash mobs levels you up and allows you to use your other abilities some of which are INCREDIBLY strong, awarding only one player the kill would hamper how long it would take to earn these abilities.
As it stands already I usually don't unlock my 4th ability until the game is basically over and we're running down the last guy or 2 alive on the opposing team, and if I'm going against bots forget about it, I'm lucky if I get my 3rd ability. (these are usually 10-15+ kill games too)