Those kind of assumptions are highly idealistic and theoretical, usually don't hold true in the real world. It depends a lot upon the talent of the people invo

Those kind of assumptions are highly idealistic and theoretical, usually don't hold true in the real world. It depends a lot upon the talent of the people involved, their past experience, their knowledge, and so forth. It also depends on the systems in question. The amount of effort needed to build some particular functionality can vary immensely between two experienced developers working for the same organization on the same system. It usually varies even more so when multiple organizations are involved, or multiple systems are involved.