Dear Danish. To some extent your analysis is very fair. One thing that does drive up DHA prices, sometimes unreasonably, is the brand premium. DHA, even though there is nothing extraordinary about its development, is a status symbol and that drives status conscious wealthy individuals towards it, ignoring places on highway that you have mentioned.
Although Zone I area is still very much considered the gold standard (again exaggerated), but once you move out, there is no brand which falls in the class of Bahria and DHA, no matter how much the wannabe societies try. Even then, I am a bit concerned with the growing trend of short term speculative investors entering blocks K-P.