No company has ever successfully achieved a total monopoly. Black markets still existed, and furthermore, they often only got rights that bumped them up to 70% of market, 90% of market. Those rights were granted and enforced by the government.
Also there is no reason to believe one company dominates over time.
COmpanies rise and fall. Peoplea re born who want to start new companies. New wealth is generated, and circulates. Small companies. Big companies. Big companies have unexpected shortcomings, get outcompeted from time to time, lose share, lose relevance. New fields or industries emerge that replace them.
A coal company can't dominate forever, it's impossible. Eventually, people will prefer nuclear, and other energy systems.
A system where you can legally stop others from having an easy time entering, where you can make it illegal to make the same things as you, where you can make it so only the wealthiest can avoid criminal consequences, where you can make it so only the wealthiest get billions of dollars in aid and so on, is not a system that is less likely to result in monopoly. Even if the system has the potential for this, it's still worse than a free market. Again, all your arguments are based on assumptions, and also ''the worst thing that could happen is the state''.
There is no way to dominate the market entirely if you are high cost, high quality, fast work. Because folks want cheap work. Some folks don't mind slow. Some folks want fancy work, not good work. They want luxury work. Some want whatever is good enuf to work. It's not as straightforward as there is only one kind of service.
Furthermore, you're not reasoning why this would be bad.
An entity provides immaculate service that is so good, no one else prefers it. They offer it at a price no one else can match for such goods. No matter who starts up, they can't be beat.
What do you think would happen as soon as they radically altered this contract or service? What do you think would happen as soon as they made this not true? That someone could beat them if they started up? That someone could match them? This can't happen in a statist regime; they can literally outlaw you. They can make it illegal to use the same ideas, etc.