Average productivity per manufacturing worker in the US grew on average by 3% per year in the 1950–1980s and 4% per year in 1990s (https://www.bls.gov/opub/mlr/2002/06/art4full.pdf), i.e. its current output is comparable with that of ~50m people working in 1969, so a 30% decrease in total manufacturing employment was probably well compensated for (putting aside the social welfare point of view).