First off, zombies AA is TOTALLY different than MP AA. Zombies AA is more like a legal aimbot. if you do not believe me, train a horde of zombies and shoot while zooming in and out rapidly and you will see that you will aim at the zombies as if you had aimbot. This helps players to kill them faster, and more efficient because the AA aims for their torso and up. In MP, the AA is much lower and switching from zombies to MP can be a big jump from having a lot of assistance to nothing at all. In MP, I barely notice AA as i usually run and gun with a sensitivity of 14 and 10 in previous CoD games. With such a high sensitivity, AA doesn't really help much as I am usually the one aiming at the target and not the AA, but AA helps me in some ways, like aiming farther distances, AA helps me get the to general area of my target and all i have to do is shoot and adjust my crosshairs onto the target. But I wouldn't really blame the AA for have off days or your accuracy. I blame myself or the connection (sometimes) not all the time. Like in the beginning of Black ops 2 i had a 2.0 Kdr but now i have a 1.60. could be the connection or it could be me. But in previous CoD's, I have a 1.90 Kdr in Black ops, a 2.09 in Mw3 (used to be 3.11 but i used the fad and got all the titles for it, but i couldnt handle the recoil anymore and so my kdr went down). Kdr used to mean a lot to me but now it doesnt because i'll have a good day and go 28-7 and then the next game, i'll go 20-18. Therefore, you cannot really compare the two AA as they are totally different.
For example, you could have the same percentage of AA as any other player, but in Game A you had the best accuracy out of the lobby, you were aiming perfectly fine and were adjusted to the recoil so you were able to control it. But in Game B, you could be playing the same as you were in Game A, but the recoil was adjusted and so your accuracy was degraded and therefore, you didnt do as well as you thought you would.This is a theory not a statement or a conclusion. Just speaking my thoughts and there will always be different views. Good luck in Zombies or MP, which ever you choose, I support you 