Carrying pallets 2 high is a high risk, hence the fact LF licenses are high risk licenses. obstructed view is not an issue as driver should always face direction of travel which in this case would be backwards if in a counterbalance or business as usual in a reach truck. Yes weight shifts when cornering which is why operators corner slowly as per manufacturer specification (and common sense for anyone with a clue). If an operator is unable to clearly assess the safety of carrying a double stack then I would seriously question the validity of their holding a license in the first place.
Section 28 of the 2011 harmonised work act puts the onus back on the worker not the trainer or the PCBU. Quite simply if you aren't competent to carry out the task of carrying a double stack then just take one pallet, you are the state licensed high risk operator...