I've not read the post but I think it is fair to say that Freelancers have more chance of being unreliable than agencies just because of the law of averages. It stands to reason that one person, trying to run a business as well as perform a job, who is likely to get people dick them around for money, etc could well turn out to be less reliable than a team of people.
But every single agency I have had worked for has screwed me, and the end client. No one I have ever worked for knew, or cared to learn, even the basics of what they were selling - and had the cheek to charge extortionate amounts which very little of gets paid to the person that has done the work.