Their main job was to help protect carrier groups.
No, their main job was to protect convoy groups. The main reason why they're used to screen carriers now is because, in the current threat environment, they're cheaper than putting a destroyer or cruiser in there.
And they were heavily involved in Operation Praying Mantis (the "Tanker War") and in protecting oil rigs and tanker convoys in Desert Storm. You can basically think of oil rigs as stationary convoy ships.