If I'm not mistaken, Keith is saying that the peg should be weighted so that we have a stable platform to push against during the steering phase. He is not saying that we should be weighting the outside peg throughout the turn.
On page 51 of Twist II, Keith says "Allow your body to relax immediately after the steering action is completed. In fact, ideally, you would be loose right when the tires 'bite,' at the moment you are at full lean angle." emphasis his
Then, on page 52, he talks about laying on the tank under the 'Sit Still' section. In this story, he is relaxing so much that he is putting his weight on the tank throughout the mid-turn phase. This causes problems later on, but it is because of the degree to which he is laying on the tank combined with a lack of suspension adjustment.
In Chapter 19 of Twist II, the main headers are "Steering" and "Pivot Steering."
The riders weight must be in the same place every turn, every lap in order to facilitate consistent throttle behavior on exit and predictable suspension behavior mid-turn . A rider can easily shift 50 to 100 lbs on the outside peg during a short steering motion but the rider cannot be expected to keep that force on the outside leg at all times. It is simply too much effort and it will contribute to early exhaustion. In my view, the answer is to steer by pushing against the outside peg and to shift weight into the saddle as the cornering forces push the rider into the bike after the steering action is complete. This is consistent with racers occasionally having the outside foot slip off of the peg mid-turn. That foot wouldn't slip off without issue if it was heavily weighted at that moment. I haven't been watching races for very long, but I've never seen an outside foot slip off during the entry or steering phases of a turn.