The article mentioned that an owner can make $300k if they have 40 vans and 100 employees. $300k to manage 100 employees and 40 vans does not seem like a lot. Grant it, some people make more money managing smaller teams in a big company, but managing that many employees and equipment for your own company versus for your employer is a lot different. You have to take on more risk as an owner than as a manager for a bigger company.
Having only one client at that scale would be very scary. At what point do they say well 300k is too much. Let's make it 250K this year.