I'm doing contracting work for multiple different customers, long-term project, and I generate 100-200k of revenue on a yearly basis from that. That leaves me with slightly higher salary than if I'd work for a boss, but I have tonnes, and tonnes more freedom and time for my kids. It's just not possible to scale that past 300k/yr, because there's only so much time you can sell.
Once you have a product, you can scale it through the roof, since a digital product, if set up well, has negligible costs, will allow you to earn way more, but only if you find something that people want bad enough to pay for and a large enough group to pay for it. Loads and loads of people have the skills required to build a product, but not a lot have the right idea and marketing to go along with it to make it a success.