More directly to your question, for a giganto consulting shop like Deloitte, the tech stack is whatever the client wants. They have people for everything. They'

More directly to your question, for a giganto consulting shop like Deloitte, the tech stack is whatever the client wants. They have people for everything. They'll also lie and say they have people for anything they don't have, then outsource it again. Even in the hyper-niche field I was working in, we weren't the only team in the company working in that field. Do not underestimate how little the left hand knows what the right is doing in a partnership-organized company. The people I worked with in my niche were some of the best people in the world at that work. The failure to deliver projects was 100% a problem of management. Deloitte has so many fingers in so many pies that you literally spend two, separate weeks every year letting them paw through your financials to see what stocks you and your spouse own, what business interests you have, to make sure there is no supposed "conflict of interest". It never came up for me, but theoretically I could have been barred from working on any particular project if, say, my wife's 401(k) had an index fund that had stock in the client company.