This is the case in many fields but not in Economics. There is little incentive to pad out PhD counts for cheap labor since the vast majority of the Econ PhD is either taking classes in first and second year or working on independent research after that. All job market candidates are expected to have a solo authored paper on the market with some asterisks I won't get into. There is little in the way of big labs or PIs who require endless RAs. To the extent we need RAs it's often undergrads or predocs doing data cleaning stuff.