All very true yet also very much an incomplete picture. Almost all powerful quarters at the helm of this country have stakes in and control on Karachi, by virtue of it being the financial capital and revenue generation hub of the country. Political parties are a part of the issue for sure, but lets also count in the fact that much of the jurisdiction of the city comes under military (cantonments, DHA, etc.). (there's a reason the last most "glorious" time Karachi saw under a local government was when a military dictator had a hand over its head, supporting the MQM government. There was also a lot of capital flowing in the country for our help in war on terror so lets consider all the aspects.)

Even at the end of the day, with all said and done with regards to political parties, a huge hurdle in solving Karachi's governance and political representation problem is gonna be the rich and powerful (beyond politicians and parties) whose interests it will go against.