Unwinding 'Systemic Support' from Big Bank Ratings

I've always been perplexed at how the big credit rating agencies respond to the distress of a large bank: typically they might reduce the rating from, say, AA to A. Meanwhile, smaller, better capitalised banks with higher quality assets that are not in distress are rated lower, e.g. BBB. Now I would have thought a financial institution that is so weak as to be getting official financial assistance should be rated something like BB or less by multi-notch downgrades -- after all, a bank's liquidity situation can change rapidly should it strike trouble!

In a world of official financial assistance to large banks in difficulty, creditors are effectively sheltered from credit risk, and this explains the higher ratings. Since these elevated ratings rest on bad policy, is it a bad thing if ratings are bought down a notch in recognition that NZ banks aren't to expect it in the event they falter or fail, as a result of steps taken to avoid this bad policy?

Today's article Bank failure plan may pressure ratings: Moody's, Moody's confess a 1 notch rating allowance for 'systemic support'. Although this seems fair and correct, the business end of the policy is at the time when an institution is suffering some distress, and is not bearing up well under pressure: in these conditions I would hope that the ratings would be dropped sooner, further and faster, implying stronger market discipline and a stronger banking system.