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
Ethnic cleansing is a strong term to use, but at inception of Pakistan migrants had a lot of say in in terms of government policy and there are many examples that they decided things despite opposition from local population.
Firstly, the reason why they had power, is that in early days of Pakistan, military beaurocracy had not yet involved in affairs of state, military came in only after Ayub came to power. The feudal lords could only exercise their power in two ways, one over their subjects in villages and second through their voice in parliament. Both had zero impact on government policy and job situation. So in absence of military power and fuedal influence, the civil beaurocracy had un-opposed power.
There are many examples of this power. For instance Sindhis bitterly opposed separation of Karachi from Sindh for being the capital, but it was done nontheless. The high qouta of migrants created by Liaqat Ali KHan is another.
It was only for these disproportionatekly high oppurtunities for migrants compared to locals that while migration of people from east Punjab to west punjab completed in just a short time, it continued for rest of muhajors well into 50s.
And advantages gained over a decade cannot diminish over few years.