You highlight a comment and I don?t understand why. Is it not PSIA teaching through and though? Point your feet, turn your legs to point the skis, turn your feet, are these not PSIA main stays? Are you confused about PSIA or are you confused that it doesn?t work, except to create skidding?
You can't have it both ways, support rotary movemetns and then realize they don't work to advance a skiers abiltiy.