The F2000 may not pack a punch like the other two assault weapons, but it does have it's advantages. First of all, the noob-tube which we all dispise. When used at a distance it really helps scatter the enemy and can create just enough pressure to push forward into a better attack position for a squad. It's good for making the enemy run into the open to find different cover. Secondly, the scope is an added advantage. Thirdly, the flashbang, when used tacticly, greatly increases your kill probabilities. If you don't believe me, just flashbang the back alleyways of Karkland or a similar map. When you have 4-5 enemy troops unaware of their surroundings due to one going off, they are easy targets. Two taps to the head and they are down.
EVERY weapon in the game has an advantage, it just matters how you employ those advantages to your benefit.