@ Rainy - Firstly, I did not recommend a book on 'theology', but on systematic theology, which is not quite the same thing. Secondly, I suggested it as a third option after both the Bible itself, and any recommended work contra cults. It goes without saying that the Bible must always take precedence over any works of man.
Finally, I only recommend such books in the specific circumstances of a believer who is particularly concerned about avoiding and discerning error. I would never recommend a book - any book - as a substitute for the Bible, but rather as a tool to meet a specific need.
The rest raises some interesting questions, but they will have to wait for another time. I'm still dealing with a huge backlog of other points raised over the last few weeks.