Except that monopoly is merely a government grant of privilege that doesn't exist on a free market at all. You say there were all these monopolies and yet fail to include any examples.
First, monopolies would have to be universally the creation of government grant privileges. There could be no other method of creation for your argument to be valid. Your article doesn't demonstrate its conclusion. It simply argues it by showing us an example of government grant privileged and then insisting that no monopoly can be made in any other way. That doesn't follow.
That would be like me saying that the only way to get to New York city is to drive there. And to prove that assertion, I give you an example of someone who drove to NY. And then following the same pattern as your citation, conclude that driving is the only method possible. The logic doesn't follow. As an example of driving doesn't exclude any other method of getting to the city. The only thing proven by the example is that driving is possible. It says absolutely nothing to the plausibility of any other method.
And your assertion is completely dependent on no other method of monopoly being possible. Exactly what your argument
doesn't prove. Leaving your methodology for checking concentrations of personal power pristinely unresolved.
Second, monopolies can be regional. You can have areas where only certain products or services are available. And every issue cited in my post would apply.
Third, monopolies were one of about a dozen system killing flaws in libertarianism. You didn't address any of them. Anti-competitive practices, no provisions to limit corruption, vast human rights abuses, economic instability, greater impact and greater frequency of economic downturns, worker and consumer exploitation, private armies, company stores, vertical integration, all of was completely ignored.
I didn't even get into the issues of product safety, the obscene environmental damage of libertarianism in practice, the pay to play legal system that ludicrously stacks the deck against anyone harmed by business, and the ridiculous disadvantage that an anarcho-capitalist society would be at in comparison to a more centralized nation in terms of infrastructure or national defense. As depending on your version of anarchy, you'd have no common projects. And no standing armies.
Your neighbors wouldn't be similarly limited. Laws and respect for liberty exist within nations. But not so much between them. In the ivory tower conceptualizations of libertarianism, direct competition militarily and in productivity aren't considered. In the real world, they absolutely would have to be. Or your neighboring country with its advanced, state funded, modern military would just come and take your shit.
And not just military considerations. In any viable application of libertarianism as a vital system in the real world would have to resolve, or at the very least address each and everyone of these issue. And demonstrate why libertarianism is better than what we have now.