Unfortunately it's true, the punishment is way too harsh and it's not about how easy or hard it is to teamkill. The problem is clear when you take into consideration the following:
1. Slow progression system.
2. Rather incorrectly designed progression system coupled with how "matchmaking" works.
To expand on the above:
1. Currently every next lvl takes quite a lot of exp, take into account that the exp rewards from games are close to nothing for the loosing team. Then for every next unlock you need more and more skill points.
2. Why it's incorrectly designed? Well, right now it's rare to play a game without any "higher" lvls. There isn't enough players and on top of that someone can always join though a server browser. Then take into consideration that the progression is pretty clear: every next weapon / gear tier is just plain better. It's not different (better in some aspect, worse in some) it's just better. Thus it creates the situation where new players are not only beginners without understanding of the game but also have no access to competitive gear and are facing experienced players with high tier unlocks. To make matter worse, players have quite a natural tendency to "want to win", so high lvl players tend to assign themselves into the same team - part of a "matchmaking" problem. I'm putting the word "matchmaking" into quotation because I don't really think you can even call it "matchmaking".
The above creates the following problem: if the player gets teamkill penalty, that player will most likely earn close to nothing or nothing at all in that match. Since the player knows that he needs to unlock new skill nods and realizes that it takes quite a lot of time to do so, the answer is clear - it's better to leave a match and join a new one, then continue with the negative score. That situation just isn't right, because it promotes the wrong behavior.
