Punjab is also 62% of population. Punjab is dew for breakup into 3 provinces, I can see that happening in next two decades... Pothwar (Northern), Saraiki(southern) and Punjab (Central)... This will be better for administration.
I don't think rigging really took place that much in Punjab. PTI is really weak in Rural Punjab, in cities they were competitive to Nawaz... If election happened today, the Rural story will remain the same. In Rular Sind PPP is very strong, no matter what happen else where, they win in rural Sind... Nawaz has being winning Punjab mostly in last 20 years, PPP lost their hold on cities after 70s and Nawaz got most of the anti-PPP votes in last 20 years.
The reason PTI gain strength in cities because PPP lost its ground completely after Benazir. After Benazir PPP don't have a national leader, most of their votes in Punjab cities went for PTI... This was not a well planned but an accident and thanks to Zardari... Other thing that went for PTI is youth votes... I don't think they were strong enough to challenge Nawaz in both cities and rular Punjab...
BTW: PTI did not sweep KPK either, they barely form govt their. Sindh belongs to PPP and MQM. Its not like Punjab is the only place PTI lost