In my preferred niche I was surrounded by a mixed bag of peers senior and junior. In turn I wrote proposals, sold work, and was staffed on projects outside my niche I wasn't experienced or qualified in, but if you squinted hard enough you could say I had transferable skills toward.
For the most part my projects were successful, in the sense of we didn't get fired overall and the customer paid for the work. The biggest ways to screw up were the easily caught stuff like missing deadlines, exceeding the expenses policy or padding hours, which was harder to catch but some folks were brazen and/or cunning about it.
"Yes we're an expert in that" was a phrase that wasn't ever taught but I heard often. Saying yes to anything buys you time to find the solution either by skilling up or connecting to someone with actual knowledge across the very large and well-connected employee base, or fake it if you can't. Saying no ends the opportunity.
Some of the work was mutually convenient, hey can you take care of this one weird project for me, cheaper and easier to go with a fudged service from an existing and recognizable supplier than to wade into an unfamiliar niche, go through the trouble of onboarding the supplier, and not know whether you're getting good service or not. Go with the big 4 and you'll likely get a solid C or if you're lucky a B grade service. Just the act of getting a new consultant onboarded as a supplier can take months or years at large companies. The big 4 are on the supplier lists everywhere already.
Tbh a lot of this contract and relationships stuff is valuable, you're much less likely to get a complete service delivery or billing nightmare out of one of these large firms. You can call them up in the middle of the night and they'll sell you anything. It's a little like Alibaba or Amazon but for business services.
Probably the weirdest part was finding the land and expand playbooks, in some of which they'd find and dine a "type b" personality and prop up their career in exchange for a steady stream of contracts. Basically quid pro quo, but none of it made explicit or overtly conditional, more an open handed game theory type of thing.
I took this mentality with me to a boutique shop. It works pretty well.