A good strategy: 1 background job that is long running and has a reasonably low price tag because it can be pre-empted, one high priority, short bursts of work that are paid top rate and maintenance on a number of old clients that still bring in a part of the income.
That way everybody gets value for their money and the freelancer gets a good mixture of income. You're mistaken if you think that having a freelancer with only 1 or 2 customers is good for you, in the long term you'll need to rebuild your relationship with new people because your old ones will go out of business when you don't need them for a while.
I think there are even situations where having a contract explicitly stating you are not an employee may not be legally binding if you have only one client.
To give you an idea of what I mean, the one that's in the process of falling apart took over six months of negotiation, periodic prodding, and concessions to get them to actually provide me fully signed documents so I could start work. The whole time they were telling me how excited they were about the project and how important it was to them. Clients like this all seem to exist somewhere on a spectrum, and you have to figure out whether they're just a 'less profitable' client because you'll have to put more work in (and set your hourly rate accordingly), or whether they're a fundamentally problematic client that will just never work out. This client turned out to be the latter, even if I am billing hours now.
I suspect once you've been freelancing long enough you can just say no to any client that seems like they could be a problem. For me, it's been a little over two years and the influx of work is not remotely enough to justify that (even if I get way more offers than I used to, and they're better offers)