If everyone were a doctor that skill would be worthless. People are (mostly) paid according to the amount of value they bring to a company. That value is relative to others in the industry. Knowing how to competently use Microsoft Office (which puts you ahead of 99% of the world population) gets you nowhere in a AI focused startup because it doesn't make you more valuable to them.
>I'm not sure wealth per person is a great way to measure economic prosperity. If you have lots of wealth, does that necessarily translate to more income down the line?
I totally agree with you here. The metric I think matters more is relative wealth. Say you are a software developer making $120,000: in the Silicon Valley that is about average, but in Kentucky that is three times what the average person makes. So in SV you live a "normal" life, but in Kentucky you are decidedly upper class.
I am ambivalent about the relative wealth. I think it is fair and helps, up to a certain level, but globally, money attracts money, which means that certain people, with certain background and certain jobs would be deemed worth leaving in California. And this relative wealth-based system is already in place (e.g. designers in Cuppertino, IT in N. Dakota, assembler in Shenzhen).
The point you made was 100% correct, but that wasn't my meaning. I said right out of med school because I meant to focus on the problem in terms of cash flow - you can be in heaps of debt but still be well off. If the world were in huge amounts of debt (negative wealth) it seems like it could still be well off.