While I understand their ruling, it does seem pretty strange and contrary to the entire career that the attachment was added to. The whole gist of the armor attachment, as stated in C&M is:
"...plates that can be sewn into clothing to give the wearer concealed armor protection. They can be added to any garment that is suitably large and alterable, and can be installed by a skilled tailor for a modest fee."
Why would that remove the carrying capacity of the Cargo Clothing, or remove the concealing features of Banal Apparel? They're meant to be discrete armored plates to enhance your current clothing, not change it into something else entirely.
That being said, the extra mods do make it seem absurdly strong, as it is basically allowing you to get super Armored Clothing (double-soak, double-def, harder to spot) for 75% of the base cost of Armored Clothing. If you also throw a Superior on there, you've got armor now that exceeds Kav-Dann/PX-11/Leviathan Power Armors (defensively, at least) for a fraction of the cost. It's a weird power-creep attachment, and super attractive to low-Brawn characters who have very little soak as it is.