Why would CB's need to be nerfed? They deal 12 damage when used during stun threshold and are pretty damn easy to hold (unless you're fighting ALPHA). CB + PB can be devastating, but CB setups are usually pretty easy to alleviate since they can become predictable.
I just think being available at +17 is to strong since You can do anything after it. Like you say, CB + PB is devastating. You don't read well and you are fucked...