Most of the successful 20th century unions weren't representing unskilled workers, they were representing skilled workers against employers so large that they had market power in the labor market for that type of skilled labor, like the Big 3 auto makers.

The problem for those workers was that although they were skilled labor, the number of employers who needed auto workers was small enough for them to act as a cartel. The concentrated market offset the negotiating power of a skilled individual, but at the same time, a company that employed a third of the auto workers in the country couldn't just replace them all if they went on strike.

But that was kind of a pathological circumstance and the better solution in that case is to do some trust busting. Or if competition increases on its own as it did from the Japanese automakers during the oil crisis.

The closest thing to that in the modern economy is the relationship between app developers and platform app stores. It's the same sort of cartelized market. But some trust busting would work there too.

And other markets don't look like that. If you're actually an employee of Google or Apple, they don't have anything like market power in that labor market, because it's the same skillset to go and work for Facebook or Microsoft or Netflix or a million other places including a large number of smaller companies and startups. And if you're a worker at an Amazon warehouse, it's not skilled labor.

> My understanding is they've been sharply eroded, but minimum wage and a 40 hour work week alone seem like incredible improvements.

Most of the claimed victories were symbolic, because they were things that were happening anyway and then legislators passed laws requiring them after they'd mostly already happened so they could say they were doing something.

Workers expect to be paid more to work 80 hours instead of 40, so given the choice between paying one worker for 80 hours and two workers for 40 hours, employers found the second option led to higher worker productivity and reliability because the workers weren't constantly exhausted and making mistakes and didn't as often quit from burnout.

Around 2% of people in the US make minimum wage. In other words, ~98% of employers pay more than that even though the law doesn't require them to, because the market does. And even without minimum wage, the other 2% would be making around the same amount of money, because the employer still has to offer enough to get the employee to accept the job.

Minimum wage is even harmful to employees because it forces them into bad trade offs they otherwise wouldn't have taken. There might have been a job paying $6/hour across the street from your apartment, but it goes away if minimum wage is $7.25 and then you have to take a job at $7.25 which is an hour away and costs you more than $1.25/hour in commuting expenses, plus the lost time and significantly increased risk of a car accident.

Likewise, the limit on hours or requirements to pay overtime can hurt workers, because if you need the extra hours, people end up taking a second job instead, which still doesn't pay time and a half but now you have two commutes instead of having one commute to a single job where you take two shifts.

The things that help workers are the things that actually increase their negotiating power. Artificial price controls don't really do that, because when your negotiating power isn't actually any better, you just end up forced to accept worse terms on some other dimension, like the longer commute.