Thanks for summarising my 5 paragraphs into 2 lines. Secondly, Yes, i agree with your reply related to Ummah. Core reason...The PAF might be open to collaborating on various subsystems (e.g., engine, radar, missiles) or technologies (composites fabrication), but when it comes to the design and development of the fighter, it seems the PAF prefers going it alone.
The main reason is to minimize risk (when you have multiple stakeholders, the complications and in-fighting go up) and to expedite the project, especially as the doors on off-the-shelf jets close. This is more of a project management issue than politics.
The concept of the Ummah is from Allah (SWT) and hard-coded into the Qur'an, it's not going away. The problem is that its application by Muslims is faulty, and that's because we're trying to mix water into a glass of dirt, therefore creating mud instead of water. For as long as the wrong sort of people are in charge of affairs, we'll not realize the concept -- or the benefits -- of the Ummah. That said, we shouldn't stop trying; God gives the honour to those who do His bidding, and if we stop trying, then we might risk losing His support.