I was wondering, why every guide says 20 APoC, when I was just fine with 9. No worries my barb is already geared enough.
Because in many (most?) cases 9 APoC is not enough. However, it obviously depends on your other stats. If you have a higher crit chance, maybe even close to cap of 75 which is easy to reach with the help of Deep Freeze/Pinpoint Barrier, you won't need as much APoC. It also depends on your APS to some extent. However, there has been a lot of theorycrafting and testing and so on (just look at all the contributions Loroese has made), and in many occasions you just run out of AP with one APoC piece. And if you run out of APoC, your performance significantly decreases. You can try this out using one of the CMWW simulators - and you might see a DPS increase by adding some more APoC, and also a better stunlock.
Because in many (most?) cases 9 APoC is not enough. However, it obviously depends on your other stats. If you have a higher crit chance, maybe even close to cap of 75 which is easy to reach with the help of Deep Freeze/Pinpoint Barrier, you won't need as much APoC. It also depends on your APS to some extent. However, there has been a lot of theorycrafting and testing and so on (just look at all the contributions Loroese has made), and in many occasions you just run out of AP with one APoC piece. And if you run out of APoC, your performance significantly decreases. You can try this out using one of the CMWW simulators - and you might see a DPS increase by adding some more APoC, and also a better stunlock.