> the outcome would have been significantly more dire had McKinsey’s proffered solution not been implemented

It's the classic can't-be-wrong-no-matter-what-happens situation. Since there is no practical way to re-run the experiment, they can always claim "at least we made it less bad." And the clients are prone to buy into it also, because it makes them look like they didn't make a bad decision to engage the consultants.

Same thing frequently seen with politicians and their supporters.