This subject has been brought up multiple times in the past. To put it simple DICE still is poor at designing their in-game challenges.
Take for example the "Combat Medic - Combat Role Challenge": Melee kills, explosive and fire damage for the medic
class? How about heals, revives and smoke deployment? Start designing your game around its core gameplay mechanics. These challenges a great opportunity to teach players how to play the game and their class and you fail to take advantage of it.