That's a simplistic, reductive, and uninformed expression of history which completely disregards the roles of the artisan, merchant, innkeeper, or any of the numerous other trades which kept early economies moving. Not everyone was a hand-to-mouth peasant farmer, either in medieval Europe, or in earlier points in history.

The building of a cathedral provided generations of employment for stonemasons, men involved in felling and shipping timber, men involved in cutting and shipping stone, as well as people responsible for feeding the workers, making and repairing their tools, etc.; and once built, the cathedral would be a draw for pilgrims, who would need places to stay, food to eat, and so on.

A cathedral provides work.