Note I mention profit before distributing to equity holders. The highest prestige and therefore most profitable consulting companies are all partnerships.
Some highly profitable consulting companies that are partnerships have very high margins, if you don't include the profit sharing component of the pay of equity partners (but do include bonus and fixed salary). The primary public source I can point to is that many top law firms publish their margins to be >=50%.
As for McKinsey, according to Google, McKinsey has 10k consultants and 2700 partners. There are 30k employees, so I give you that the overhead rate is higher than law firms. But
given how different pay is between partners and non-partners, and there is still a relatively large portion of partners compared to other employees, the margins, if calculated this way, is probably still pretty high.
Now is this the right way of considering profit margin? There are some good reasons to disagree with it. But in the same way people can like or dislike EBITDA. At least, it's like nobody discounts Larry and Sergey's cut from Google's profit.
In this context, I would argue it is indeed a good way, especially for the purposes of discussing the discrepancy between grunt pay and hourly charge. It tells us that a very large part of that discrepancy goes to equity partners (who aren't those doing the execution work), rather than "overhead" as it's being argued. This is very different from big-corp type public companies where, even though executive pay is a lot, the bulk of the pay goes to shareholders ans a large number of rank and file and moderately paid middle-managers, which I suspect to be closer to accenture's profile.