An ATG side is usually being picked to theoretically play teams of similar strength. Pollocks batting would be about as useful in an ATG matchup as in a regular one- he would score less against ATG bolwers, but so would everyone.If you pick an ATG XI, wouldn't your specialists be so good that the need for an all-rounder to balance the side is diminished? So hypothetically I might pick Kallis as a batter in an ATG XI but wouldn't want him to bowl, or hypothetically pick Pollock as a bowler but not be expecting to rely on his runs at 8.
Kallis is an average bowler. Very useful in a weaker attack, but a really weak point in an ATG one. A 5th bowler is always going to be handy to make the rest of the attack better, but his value will be down.
I dont think looking at how a player would perform in an ATG team is a good way of assessing their quality though. How they did in their own team, or how they would do in a median strength team both make more sense to me.