hate to break this to you, but everything is devoted to protecting the carrier, even unto the FFG/DDG on the inbound bearing of the ASM making a beeline for the carrier sacrificing itself to protect it.
you can forsee many things, but frigates to protect lone merchant ships will never happen.
The idea is to splash incoming missiles.
But that was not my point, was it? It was that carriers have frequently protected other forces - as only they can put fighters or multiple ASW helicopters into the air, as long range task group weapons. Those aircraft work in conjunction with the 'escorts'.