If I were to make a guess, I'd say that the direct objective is determined before any programmer/artists are brought in. In my head, I see it like this:
people like Ian meet with higher ups who determine the big plan
Ian meets with workers, informs them of the plan
the workers suggest features
Ian and the higher ups decide what gets cut and what doesn't, based on the budgeting idea
So I don't know how big of an issue a large development team is on the planning side. I don't have any experience of that, seeing as the NCAA credits has more names than the building access internal page of my company (or at least, I assume so).