They heavily dominated beaurocracy right from 1947 to 70s and they controlled the then capital of Pakistan Karachi, till it was shifted to Islamabd in 1964.
Since I would not have the most accurate knowledge of the extent of control of civil bureaucracy the Urdu speaking people had till 1970s as you claim & I will also not have the most objective understanding as to where lied the real seat of power in those days.., the military establishment or the ruling elite so i will not comment on this any further ..., just that it does not seem comprehensible to me that the Muhajirs had such influence in those days that they could inflict 'Systematic ethnic cleansing' as claimed by the burqaX because it is just so inconsistent with the general mood being helpless & insignificant in the youth in the 80's which i will again repeat led to the political developments that followed & not the other way around