The budget lever is still available in limited forms e.g. do you devote two engineers from the team to project A or three? The point here is that the engineers have to be already up to speed on the codebase and already know how to work with their colleagues; and adding more on project A leaves fewer for project B, C, and D etc.
Also there is monetary budget. Can I solve an engineering inefficiency by throwing larger servers, or buying a licence for a relevant software service?
Maybe one could say that in the beginning of the project, one can use that budget lever, but not in the end (mythical man month)
Once the wheels are in motion you can only accelerate by breaking off sub-projects/teams... but if you're at a point where this can accelerate you, it means you were already slow-as-hell :|