In my experience working with a well-known consultancy that uses strict XP, agile, TDD, the whole 9 yards - this isn’t the case at all.

They talk about a triangle of (scope, quality, cost) where you can only pick 2. As a business you can choose what trade off you want to make, but no one’s promising that you can have a rocket ship by next week with 2 engineers if you just organize your tickets correctly.