Yep, as I've stated previously, the days of close US/Pak military cooperation are slowly drawing to a close. The Viper will be the last piece of major defence equipment Pakistan will purchase from the US, let alone other Western sources. Given the current situation in Afghanistan, there's no hope in hell any more Vipers are coming to the PAF. In my view, there has been a tacit agreement between the US and Pakistan of the Taliban either regaining control again, or some form of coalition government. In any case, the Pak military would prefer influence in Afghanistan (to negate indian and iranian presence) at the expense of any further Vipers.
But what is more pertinent is that it also implies no more attendance of the PAF at Red Flag exercises, or any other joint US-PAK military engagement, when the PAF transitions to an all Eastern/In-house airforce. The success of the PAF has in large part been due to the influence of US training, tactics, and doctrine, and the PAF wouldn't be what it is today if it were not for the influence of the US. The PAF will soon lose that exposure to US influence and largely have to adapt Chinese origin equipment to its own doctrine from now on...good luck with that.
As for the QUAD...well, clearly the US hasn't learnt anything itself over the past 30 years