Your advice, while logical, has a small problem. A coder usually has a history/reputation on this kind of sites. Once you stop using it you start basically from zero. The reputation is not transferable to similar websites.
Importantly: it is both not true that your reputation will necessarily be improved by working for charities/contributing to OSS, and not necessary that one has "a reputation" to successfully get consulting gigs.
To get a consulting gig, you need to a) identify a person who has the authority to say yes to a consulting gig, b) convince them to say yes. Even if you have a reputation, you don't get to skip these steps. Reputation as being among the top in the field will get you more inbound leads, but you'll still have to sift down to people who can actually say yes to gigs, and then sell them.
How do you think your average accountant sells accounting services? By having a reputation as being one of the best accountants available for hire? No. They meet with business owners, winnow down to the ones who have money and problems with it, and then say that they'll trade solutions to problems for money.
Besides, he might be able to refer new customers to his old history (I hope, I haven't used Freelancer).
The ultimate goal of any agency-type business is to take the maximum amount of money from their clients while doing the least possible amount of work for them. If the clients feel locked-in (as you do), that's brilliant for them, because they can abuse you in this way and they know you won't change your behaviour apart from grumbling on some forum.
Although others are suggesting you use a competitor, I think you should consider whether this is a business model you want to support in the future.
Reputation is, by definition, how people see your work, experience, and ability.