I've read Milestones pretty closely and here is my impression of why Qutb blows off the importance of well designed governance.
(from the web site http://gemsofislamism.tripod.com/milestones.html )
So what political system then does Qutb favor?
"God's rule on earth" - the Shari'ah.
The way to establish God's rule on earth is not that some consecrated people - the priests - be given the authority to rule ... To establish God's rule means that His laws be enforced and that the final decision in all affairs be according to these laws. [p.58]
But God is not going to descend to earth to administer His law! Actual human beings will have to do it. How are these judges/administrators going to be chosen? How will they handle disputes over interpretation of God's law?
This, of course, is a matter of great interest in Islamist republics like Iran (and formerly Sudan) where there has been considerable and sometimes violent disagreement over just what is God's law. What does Qutb have to say? He only asserts that it won't be a problem.
God's religion is not a maze nor is its way of life a fluid thing ... It is bounded by those principles which have come from the Messenger of God ... The principles of Ijtihad and deduction are well known, and there is no vagueness or looseness in them. [p.85]