That the state which grants you your right can take them away doesn't make them flimsy.

And it's certainly more than "hardly" a monopoly. If the government gives a certain company right to operate on train track infrastructure but denies the same to every other company, then does that first company hardly have a monopoly?

Large companies that have money lobby governments to ensure they do not threaten their monopolies. Individuals can't do that.

Sure. That’s how rights work. It’s why we need to keep on fighting for them when necessary.

By that standard, nobody has any right to anything. I think it's pretty widely understood that rights range from aspirational descriptions of a just world to widely accepted legal consensus.