As someone who worked with McKinsey consultants in a past life, this seems pretty spot on. The partner and one of their associates were sharp. The other associate mostly got arrogant. They were brought in around a new product line I was the product manager of. Yes, they spent lots of time interviewing us and basically validated what we told them.

That said, they presumably gave executive management some warm and fuzzies that we weren't smoking weed. Sure, they could have just taken our word for what we were telling them, but having a second pair of eyes is actually not a terrible thing. (And it's part of what I did for clients in a subsequent job.) They also gave our business planning people some complicated financial modeling spreadsheet which kept them busy and mostly out of our hair.)