I have freelanced for about 15 years, programming and system admin for US companies.

The author describes a kind of freelancing I usually call piecework. That means finding and bidding on small jobs constantly, often on race-to-the-bottom sites like Upwork. The hourly rate quoted ($25 - $35 per hour) seems very low for an experienced freelancer in the USA, but typical of piecework rates.

Full-time jobs may look more stable and predictable, but only until you get laid off. For the approx. 250,000 American tech workers laid off in the last couple of years, now left with no income or insurance, losing a full-time job probably looks even worse than freelancing.

Rather than constantly churning projects and customers, a successful freelancer will optimize for long-term customers, providing business value and not just small one-off tasks, and more predictable billing arrangements such as retainers and fixed-price bids. Hundreds of thousands of small to medium-size businesses don't have any full-time IT staff so they rely on outsourcing. Once they find someone who cares about their business and offers ongoing value a good freelancer can keep them for years. You only need a few long-term customers to sustain a freelancing business and make more than most full-time employees.

Having specialized skills helps a lot, but so does knowing how to talk to and listen to customers, how to focus on solving business problems rather than a "tech stack," and how to cultivate long-term relationships. These days "specialized skills" can mean knowing how to do anything other than React or Python, the bar seems fairly low. Managing small company cloud infrastructure, for example, seems very much in demand with relatively few people able or willing to do that work. I know freelancers making a good living setting up and maintaining WordPress sites.

Taxes, insurance, etc. all turn into your problem as a freelancer. You also get quite a few good tax deductions as a business owner -- including deducting health insurance premiums -- so with the help of a decent tax accountant you can figure out how to reduce taxes. The self-employment tax the author refers to (USA-specific AFAIK) mostly means Social Security and Medicare, which freelancers and all self-employed people have to pay 100% themselves, though those amounts also get deducted from federal taxes.

Health insurance in the USA does present a surprising cost for people used to their employer paying for it, but the cost varies mostly by income, and alternatives exist for younger and healthier people. US medical costs, including insurance, drives retirees and digital nomads to live abroad, where they can more easily afford medical care. Only the influencer crowd tries to pretend they work on a laptop from the beach -- no one should take those people seriously. Social media influencers do not freelance, they try to make money from influencing.

As for scaling, yes, the number of hours in the day and the freelancer's tolerance for work limits scaling. Rates can get very high for people with solid in-demand skills, hundreds of dollars per hour or even more. If you want to scale by building an agency or consulting company you change from freelancing to building and running a business, with everything that entails. I have never wanted to scale up, only to make a comfortable living, but I know freelancers who have scaled their business -- which really comes down to doing the tedious stuff like marketing, billing, taxes, etc. for people who can't be bothered to do that themselves.