I am sorry if I misinterpreted what you were saying.
But we do seem to have diametrically opposed views.
You pay a union worker more, that means that everyone else pays for it through higher prices.
You pay a union member more and they put more into the economy creating more opportunities for local business - the economy is circular.
Union membership has taken a nose dive since the 1980s which also correlates with the nose dive in share of company profit with workers. Insecure work is at much higher levels now which again correlates strongly with this.
I'm not arguing that union's have their fair share of mediocre workers, I would argue that they protect all worker's including the mediocre ones and it's better to protect everyone than no-one.
I would argue that there are just as many mediocre workers in non-unionised workplaces, they are everywhere and being in a union is not a predictor of this.
We get mad at businesses for monopolies, yet a union is a monopoly on labor.
I also disagree with your stance regarding unions create a monopoly, this makes no sense. It's the same as asking medium sized companies to break up into smaller companies because they have too much power - unions give poor workers some negotiating power rather than none which on the whole produces better results for society.
Silicon valley comment - is an outlier / strawman , I'm not advocating programmers who are making outlier amounts of money need to implement collective bargaining (which see below is different from a union).
You talk about unions as though they are a monolithic organisation and all unions are the same, this is certainly not the case.
I've been a member of a union for five years now, I treat it as a democratic institution that makes society stronger it keeps a balance between capital and labour.
I do not agree with the direction that the union takes sometimes but that's ok, it's democratic and I believe collectively we can work together and make things better.
I don't belong to a union that stops non-unionised workforce but I am in a union that demands and fights for minimum conditions for all workers especially the most vulnerable. I have never been part of industrial action either!
I've worked non-union workplaces including startups, commercial property, travel, professional services and I'm currently now working at a university. I don't fit into any of the categories that you have mentioned of a union worker. I am certainly not mediocre or average in my workplace.
And unemployment rate? Before corona skewed everything, the US unemployment rate was below 4%. In Sweden? Close to 7%.
I don't live in the US but I look with utter fear that my country will follow America's workplace relations.
Sure it works well if you earn good money (see Silicon valley worker) but the way the poorest workers are treated in the US, that is the stuff of nightmares.
Having to have two or three minimum-pay jobs just to be able to survive in the 'richest' country on earth is certainly a dystopia that I hope my country doesn't follow.
I don't think all unions are good, or make good decisions in the same way I don't think all business managers are good or make the right decisions. They are just humans making decisions and taking actions, some are good, some are selfish and bad, most probably in the middle.
But unions on the whole do ensure the lowest paid and the most vulnerable have some power and leverage in a society that based on a lot of history has not cared how they fared.