Yeah, I'd say it depends on the skill of the player. I am, what I would consider to be, an average player. I am on the bloodthirsty part of the challenge for the KSG, and I have about 800 kills with it. So, considering that there players much better than myself out there, I'd say it's possible, especially if they were getting the good side of the lag comp system. Where as, when I started with the shotgun, I quickly realized that I am not getting the good side of it.
the first shotgun was for me the easyest because you dont need to aim perfectly to get the guy killed u walk around a corner and boom kill. ksg is bit more tricky