Of course you would have been trained to fire LAWs in volleys against modern tanks, and still got few chances for a kill.
Now what about firing at an APC or a truck? Standing? At 50 meters range?
The game rules must be flexible enough for any kind of situation, and you run soon enough into some that are quite not 'out of the book'.
One game turn is 3 to 4 minutes, and there is no clue about what happens when. As I wrote previously here, when your inf squad or AT team fires 3 or 4 LAWs at one AFV before scoring a hit, you can assume that it IS a volley fire indeed. Time just doesn't run linear in a turn-based game!
And from what I have played until now, LAWs seem well balanced enough, and if you ran their specs down, you would end up with very poor AT abilities in your squads.