While I generally agree with what you are saying, it is very important to understand that built-in types are not magical. This is where coming from a low-level embedded C or assembly background can be very useful.
As an example, there are a number of sites showing the performance hit you take if you use some of the NS types in Objective-C. If I remember correctly, in some cases you are talking about NS types running 400 times slower than alternative code.
In my mind, the question of data representation could also include this very choice: Do I use an NSArray or do I do it "by hand", allocate memory and use a "simple" array?
As an example, there are a number of sites showing the performance hit you take if you use some of the NS types in Objective-C. If I remember correctly, in some cases you are talking about NS types running 400 times slower than alternative code.
In my mind, the question of data representation could also include this very choice: Do I use an NSArray or do I do it "by hand", allocate memory and use a "simple" array?