That is just not true. They might not be able to choose the quality of the sniper/machinegunner/driver/whatever, but they sure can decide if a soldier is trained as a machine gunner or as a sniper. Which is one reason I don't like the class system. Here a sniper is a sniper, there is no difference between two snipers at the start. They both have head shot (IIRC), and that is it.