The economy is not wealth and so GDP fails

GDP measures the size of the economy but it does not measure wealth... to measure wealth we must include everyone but the economy only includes the wealthy (those who are involved in the economy). It is perfectly possible for a large segment of society (the poor) to be excluded from measures of GDP because they do not make significant transactions. GDP measures transactions which will exclude the poor. To measure wealth we must include everyone which GDP fails to do and so GDP fails as a genuine measure of wealth... although it does measure (the size of) the economy perfectly adequately. The economy alone is not wealth and so GDP fails as a measure of wealth.