How is "there's no downtime in cooking" better than "Cooking onions is not downtime?" Both are assertions without backing evidence. For instance, it's possible

How is "there's no downtime in cooking" better than "Cooking onions is not downtime?" Both are assertions without backing evidence. For instance, it's possible for "Cooking onions is not downtime?" to be true (e.g. cooking onions requires active work) while "there's no downtime in cooking" is not true (e.g. cooking chicken broth involves downtime).