It's not an American perspective; it's an economic perspective. The parent comment isn't talking about people's psychological wellbeing, but "how people actually live" (in terms of do they live in poverty or like rich people).
Wealth doesn't capture that. For example, you might have someone living in extreme poverty in Guatemala who has no electricity or running water, a small home with a mud floor, and eats mostly rice and beans and similar. If this person has no debt, they might have a very small but positive net worth. Meanwhile, you can have someone from America with negative net wealth living a middle class life. The Guatemalan might be spending the equivalent of $600 per year, while the American might be spending 50x that. Looking at spending better captures who is living in poverty.
Wealth can also fail to capture how the wealthy live. Warren Buffett is notoriously frugal. Looking at wealth, you'd find he's about 180,000x wealthier than the mean American adult. Yet he has one house which he bought for $31,500 in 1958, and apparently eats breakfast at McDonald's each morning for no more than $3.17. The vast majority of his wealth will be going to charity. Looking at his spending gives you a more accurate picture of how he lives than looking at his wealth.
Wealth doesn't capture that. For example, you might have someone living in extreme poverty in Guatemala who has no electricity or running water, a small home with a mud floor, and eats mostly rice and beans and similar. If this person has no debt, they might have a very small but positive net worth. Meanwhile, you can have someone from America with negative net wealth living a middle class life. The Guatemalan might be spending the equivalent of $600 per year, while the American might be spending 50x that. Looking at spending better captures who is living in poverty.
Wealth can also fail to capture how the wealthy live. Warren Buffett is notoriously frugal. Looking at wealth, you'd find he's about 180,000x wealthier than the mean American adult. Yet he has one house which he bought for $31,500 in 1958, and apparently eats breakfast at McDonald's each morning for no more than $3.17. The vast majority of his wealth will be going to charity. Looking at his spending gives you a more accurate picture of how he lives than looking at his wealth.