unions

I feel that the distinction is made wrong. All these labors shown may not require much of a formal education towards the job, but they all require skill that will be refined significantly over time.

• Somebody who works as a harvester for years is much faster at picking crops and much more efficient at seeing which are ready to harvest and which arent.
• Anybody who has kids knows that it takes years to traing them, how a properly cleaned house looks like.
• Cashiers who are familiar with the workings of the companys systems, who know the numbers of bread, produce and other non-barcoded goods by heart are much faster and have less situations requiring looking something up. This in particular are skills that simply require on the job time and experience. The same issue exists for engineering project managers who cannot learn all the PCA codes of their company in the first week.
• Everyone knows the difference between bar-staff that knows how to properly draw a beer and those who don't.
• Fast food workers need to perform consistently in a high stress environment, and keeping taps on the fries, the burgers, three customers orders and dealing with the half-broken coffe machine is a skill many CEOs would lack. Same goes for waiters in restaurants
• Being a good brick-layer takes years of practice. A well built brick wall with consistent gaps and a smooth surface is difficult to achieve, and both aesthetically and structurally important.
• ...

Finally many of these jobs also require social skills and provide socialisation as part of the experience. My favorite barkeeper manages not only to get everyone their drinks in a packed bar, but also chat with the regulars and newcomers while at it. People could just order take-away instead of going to a restaurant. But having a nice restaurant atmosphere is part of the experience and the result of good waiters and so on.

We accept experience as a relevant salary and position argument for "high skilled", which should be called "high educated" labor. It is equally relevant in supposedly "low skilled" or "unskilled" labor.

There are some jobs that can be done with essentially no training or skills at all

I disagree with the use of the word "skills". I think any job not involving any skills at all (carrying things from A to B for example) disappeared decades or centuries ago. Every job now requires at least some skills. I certainly could never do a lot of "unskilled" jobs. I don't have the physical attributes for some of them, and I don't have the personal skills for others. The real issue is that while some of these jobs do require skills, they're skills that are common enough that the people with those jobs are easily replaceable. Someone who stands up for themselves can be fired and replaced easily and the replacement will only need on-the-job training.

Also, people who work in jobs that require only on-the-job training can become extremely skilled at them. But, unfortunately, that often doesn't lead to them making any more money. They're much less replaceable when they gain skills at those "unskilled" jobs, but it doesn't often lead to them knowing that they have any real power. And, often they don't. An employer will often be willing to fire a very skilled low-wage employee if the employee speaks up for themselves, rather than risk the other low-wage employees getting any uppity ideas.

As for "poverty wages", that's not really related to capitalism or to labeling something "unskilled". It's just power dynamics.

Peasants had "poverty wages" long before capitalism was a thing. They owed a lot of labour to whoever owned the land they worked on, and in many cases even if they were growing food, they were literally starving because they owed the food harvest to the land owner. If they didn't deliver, they could be severely punished or even killed. But, if you were a skilled craftsman, you could escape from that trap. You may still not have had any real legal rights, but you were likely to get a pretty high wage. There's a reason that one of the big secret societies is the Freemasons. Stone masons had power because they were not easily replaced.

Wages are about power, who had the power to demand more than just subsistence living. If you do a job that requires only on-the-job training, you're probably pretty replaceable, so your bargaining power is limited. If your job is hard to replace, you're better compensated.

The only power that "unskilled" workers have is that there tend to be a lot of them. If they joined unions, that union would have a lot of members so it would have some power. If they voted for political candidates that truly represented them, those candidates would have a lot of backers. Unfortunately, in recent decades, the uneducated low-skilled workers have been convinced to vote against their own interests. They vote for parties that scapegoat others, and then gut policies that would benefit low-wage, "low-skill" workers.