$6000 a week is $150 an hour and seems to be a pretty reasonable rate.

What you are missing is: not every week will be booked.

I've billed 10-20k in rare weeks. It's because it's a one-off project that they want you to work 40-60 hours on that week: so you can't do anything else with your business.

Rates drop a lot for maintenance and service plans where they'd like to have you on retainer month over month for years (hopefully).

This is just web development.