> Economics doesn't measure wealth

Economics measures a lot of things, including wealth. It often uses monetary units as as the units of measure for both stocks like wealth and the numerator of flows like income, but even then its not actually measuring money, its using various techniques to convert things into money-equivalents to have common units.

> which is a proxy for political power and social status.

“Wealth”, “political power”, and “social status” are different ways of saying “the ability to get other people to do things you want them to do”. They are different lenses on the same thing.

> In economics those are primary, and everything else is labelled an externality.

No, in economics “externality” is the label given to a cost or benefit accruing as a result of a transaction to a party other than a direct participant in the rransaction. These are important because they explain one reason why even if rational choice theory did hold (which it doesn’t), markets could produce non-ideal results, because market decisions are based on (and optimize in aggregate, if the assumptions of rational choice theory hold), only those costs and benefits that are internal to the transactions (that is, accruing to direct, voluntary participants in the transaction.)