Suppose country A consists of 99 peasants and 1 plutocrat. The peasants work full-time and the plutocrat consumes their entire economic output living a life of fabulous luxury. Country B consists of 100 people who work part-time and live simple lives that they can afford. Country A produces more goods and services and has a higher GDP than country B - let's say twice as high. Nevertheless it is reasonable to consider country B better-off.

Edit: The above is probably conflating some unrelated issues, so let's just simplify: country A works full-time (40hrs/week) and spends their leisure time expensively, country B works part-time (20hrs/week) and spends their leisure time cheaply. Country A's GDP is twice that of country B in the obvious way. Is country A really better off than country B? (If you're going to make a revealed preferences argument about working hours then bear in mind that there are very few less-than-full-time jobs on offer, partly an artifact of the way current regulations treat full- and part-time jobs)