There are quite a few studies out there showing that small amounts of alcohol may actually improve performance.
It depends how one defines "performance". There are studies showing that small amounts of alcohol may improve creative problem solving,
but at the expense of focus and alertness. Not a good thing when you're shooting that Cat 3 approach!
Plus alcohol
is also a sedative: it increases fatigue levels and may also interfere with sleep. So it's silly to say fatigue is better than alcohol, since alcohol leads to fatigue.
The Sunwing Captain passing out in the cockpit is a good clue about the relationship between alcohol and fatigue...