Completely agree on the not going any faster point. The Mythical Man Month demonstrates this exact concept perfectly.

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?