I’ve been both a contractor directly for companies, and contracted through contracting companies (being an employee for a contracting company is usually called being a consultant, which I’ve also been). In either case I would not assume that I could arbitrarily sub-contract my work out to others.

The ability to subcontract is one of many tests for whether you are an independent contractor or not.

In which jurisdiction? How many tests are there? How many do you have to pass?

It’s a pretty ridiculous assertion to claim that you must be able to sub-contract to be a contractor, and I’d be surprised if there was even one jurisdiction in the world where that was true. It would mean you could never screen contractors.