I'd say the initial XP farms were a predictable consequence of their unlock system.
First to unlock some guns/gadgets, you need to get to a certain level to unlock a challenge, then you have to complete the challenge in order to unlock it. This is dumb, and it should be one or the other. Either you get the item in question on reaching a certain level, or the challenge is just there and you get it after completing the challenge, or series of challenges.
Second, the weapon attachment unlock requirements are absurd. Some guy on Reddit worked it out and it's something like 3000 kills to fully max out a gun. BF4 required 510 kills to unlock everything for a gun, for reference.
