Honestly, the Navy just seems to have come to a different solution. In our view, the threat of ASW aircraft is real enough to warrant a sea-based air defence network, but these guys might be of the view that the sea is sufficiently vast enough to enable Pakistani submarines to avoid the P-8Is. It's not a bad view considering the scale of aerial ISR it took to find MH370. They'll need to be pretty confident in China's submarine acoustics against industry standard sonar, but overall, it is a valid - albeit contestable - view.
I disagree with its view, but I wouldn't disparage the Navy for having it. Pakistan has finite funding, and it is beset with fiscal uncertainty. I know people get ticked off at hearing this, but this is the reality of the situation. The Navy made the trade-off of bulking up on a strong submarine fleet, which are inherently difficult to track, at the expense of a thinner conventional frigate fleet.
@Oscar