Shenanigans. You've never worked in retail. Even if you come back claiming otherwise, I'm still going to accuse you of lying about it because you could only be more out of touch with reality if you claimed to be the ghost of Sam Walton himself.
"Necessary" staff does gets cut and the remaining employees are expected to pick up the slack. The alternative course is shaving hours off of the schedule for all employees. Sometimes they go both routes.
One way or another, the retailer will not bear that cost of increased wages. It gets suffered first by employees through reduced hours, then by customers in a degraded service experience.
You offer economic theory. I'm telling you from bitter experience what actually happens.