To the extent that a project involves implementation of existing code / modules / software and other activities that are not greenfield developments, though, the software-development-estimation-ability is not relevant as an argument against these methods, though. All training, activities, budgeting, hiring, etc. "knowable" activities around developing a project can also be managed in that way, and particularly if you're doing agile, you have a cadence against which you can do long-term planning of non-development activity.