Cables do not build muscle. They are only good for increasing TUT (time under tension). To utilize cables correctly in training to increase TUT, advanced trainees superset them with a heavy compound lift such as bench/incline presses. Cables should be used in a very slow fasion...6-0-3 tempo. Heavy weight builds muscle. ;) (not IMO, fact)
If you are using double cable flyes, you won't cheat unless you use too much weight. If I was to do 1 arm cables, I'd be fighting to keep my balance unless I decided to use very light weight.
Also, if someone with a "pigeon breast" was to use dumbbell presses, the pecs work independantly to push the same weight up, thus one side will catch up to the other gradually...guaranteed. :cool:
I'm not trying to call you out or nothing so don't take offense. I respect the fact that you are trying to take the time to help.