Interesting subject, your first two assumptions of keeping the carriers well to the east seems to be the major driver of ruling out a Harrier/Sea Harrier strike on the mainland. Plans with Sea Harrier navigation systems being suited for the task of leading a mixed air group were drawn up but never executed. I would add to the list that these aircraft were precious for air defense of the task force, so losses had to be kept to a minimum. Not so sure it would have been a turkey shoot against the (Sea) Harriers. They could have come in at ultra low level. I believe the airbase at Rio Gallegos had hardened aircraft shelters, and Rio Grande had revetments likely minimizing damage.
Invincible did one dash to the west and launched a Sea Harrier (Sharkey) that approached the mainland. I seem to recall from his book he reported seeing the glow of lights or factory IR on a pop-up.