Pakistan has way too many ethnic/linguistic intricacies to have large provinces. They must be deconstructed into smaller manageable districts. Large provinces, salivate and motivate the malcontents into fomenting trouble... politically. When polities are deconstructed people trying to egg their hatred on linguistic, ethnic or religious grounds that much more difficult. They cannot take their argument home with people having slightly different accents or ethnic makeup or religious persuasions.
Remember all politics is local... multiparty large constituencies only further divisions(even among members of the same family), create core group of supporters, reaching spectrum of fascism. Division and distinction takes you home... after all you're an individual first!
A nonpartisan electorate that serves its constituents only, replaced by them, if found wanting. Merit and honesty being key traits here. When individuals, families, tribes and ethnicities are direct recipients of, and, enforcers of their own domains, state becomes that much more secure. Remember key here is stopping any single groups national ambitions... since federation is a complex melange of all the disparate communities, it is and therefore a common cause. In the absence of such paradigm people are and will continue to be susceptible to nationalistic ambitions of certain motivated malcontents who pick and choose the narrative for lesser inclined.
Isn't it interesting that Baloch tribes live in three of Pakistan's provinces yet only seek(some) "liberation" in one that is named after them? Sindhis that inhabit again two provinces and seek only one named, perhaps theirs? Pashtuns that are equally spread out in all of Pakistan, more somewhere and less in other places... seek only a certain piece of the pie... whereas the most diverse province of Pakistan with it's multitudes of accents and ethnicities seeks no such distinction? Why? Those ethnic/linguistic distinctions may want separation from Punjab but do not share national ambitions, why?
All politics is local!
Pakistan has failed to invest on itself, improve upon itself... sleepwalking a colonial construct, creating hollow individuals not grounded in their local history, serfs of an empire that seized to exit long ago, supposedly. Why? Why takeaway people's history, narrative, national context? People defenseless against competing narratives...
Why not invest in local knowledge(existing) and build upon it? Why not invest in local languages or their derivatives and be proud of it... Is Finnish more widely spoken than Punjabis or Balochi? Knowledge about oneself creates more grounded people, capable of countering competing narratives adjusted in their wider contexts.
واعتصموا بحبل الله جميعا
Anyways, I can go on and on touching all associated tangents ... but you got the gist.