Let Alone Let Alone

It seems to me I have been seeing this formulation more often in public (virtual) prints.  This example from David Brooks's column today about America's coming dominance in gas and oil production:

“OPEC will find it challenging to survive another 60 years, let alone another decade,” Edward Morse, Citigroup’s researcher, told CNBC.

Tell me this is not backward.  The more extreme instance ought to be the one you must let alone, if even the less extreme is speculative. "Another decade, let alone 60 years."  I suppose if rapidity of threat to survival is the measure, then a decade is the greater reach.  Even so the formulation is wrong.  "Another sixty years, perhaps not even so much as another decade" avoids being, well, wrong.