I have worked with the big 4, and also been on the receiving end of their "work". I can vouch for this comment personally. I've never seen less effort put into something worth so much money. Reams and reams of documents, jargon, and other bullshit and some cheap, obviously outsourced, incredibly shitty, "wireframe" sold as an MVP of a product.
I would be impressed by them if I wasn't so disgusted.
I've also seen some of these expensive "strategic" documents. And they looked like they were written by a high schooler (not a top of the class student either).
Just how fast they can adopt their standardized, saying-nothing-of-value presentations to each client's internal jargon and "needs" is impressive so, I have to give them that.
I would be impressed by them if I wasn't so disgusted.