Earlier quoted context omitted.
It is not freeing people to do more useful jobs. It is just making them unemployed. I like self checking, sure, but the employment result of it is not better jobs.
Your theory predicts ever-climbing unemployment rates, but the prime-age labor force participation rate is near its all time high [1] and unemployment is at an all-time low [2]. [1] https://fred.stlouisfed.org/series/LNS11300060 [2] https://fred.stlouisfed.org/series/UNRATE
- self checkout was only thing going on in the economy, - cashiers represented overwhelming majority of employees.
Otherwise you are making overly large prediction from a single small data point.
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Let me say opposite theory: if self checkout would be "freeing people for more useful jobs", cashiers salaries would be raising prior self checkouts. As employers would compete for people, they would pay cashiers as much as those "more useful jobs".
That did not went on. These were and are minimum salary jobs.