What I do know is that for various reasons we struggled with direct hires and needed to grow quickly. So I guess the numbers somehow worked in its favour.
I've been involved with hiring consultants before (in UK and Norway, using consulting companies like Capgemini and Sopra Steria), and it was always the case that it was a lot more expensive - but yes, it means you have instant access to a large talent pool. It also meant that if someone didn't work out, we could swap them out with 2-4 week's notice, depending on the provider.