It's usually an internal research team, specialised in a vertical, say Energy or transportation that prepares the material for the consultant. Still, most good management consultants are good at creating docs, excels and ppts. And they are good reading/sifting through the data quickly; just like a senior software engineer can navigate and grasp code more quickly.

The larger issue that I find with management consulting approach though is that they use the same set of tools to create solutions for ALL problems. They will throw in some charts, finance numbers, pas research etc. to sell a 'story'. They usually don't work on implementation but to present the first part of the solution. That's not how every problem should be solved IMHO. McKinsey et al. can make things easy for bureaucrats or government people to grasp, but to be honest their suggestions seems pretty ridiculous at times. Just look at some of the articles they have written about software industry and how out of touch it seems. Most of their solutions on social issues and such fields are rather ridiculous too. So I would hire an ex-consultant as an employee, no problem. But I wonder if I would ever want to outsource work to a Management Consulting company.