Actually 10-11 isn't that big of a number for a country like Pakistan. These doctrines and purchases depend on the threat perception. You have a massive air-force to counter and protect your country from. So you do need proactive measures. The thought process behind the PAF leadership is that with growing Israeli influence inside the Indian military, and the Israelis having used pretty much all American systems (TPS radars), what if they can jam them? So the numbers of AEW aircraft are increasing to hedge against that. In an event like that, the entire war will have to depend on the AEWC platforms so it'll be fought from the air. Its very difficult to jam an AESA radar, especially a moving one that every few seconds can change the direction of its beams altogether and is mounted on a fast flying platform.
Next, to provide 24*7 coverage, Pakistan needs 3 AEW aircraft (to cover the land mass). So 10 hour duration plus future refueling, you'd need 6 to patrol 24*7. Its safe to assume that two are additional for maintenance support and attrition loss during a conflict (projected loss to ensure 24*7 coverage).
Then, you'll have the ZDK for naval role, with some overlapping area between ZDK's and the Erieye's around the port cities / end of land-mass. Which would still be enough for the Erieyes to get data from P3C's and other Western platforms and route them a 100 mile or so for ocean based operation from Erieye's LOP (last operational point or boundary, which would be the end of Karachi). This way, the Erieye's range being 350-400 KM still directs the P3C's and F-16's vector towards potential adversaries. The ZDK's can be used for maritime surveillance (PN ships, tracking IN ships and jets from a huge distance), as well as providing an expanded coverage platform to look deep inside India, both from around the physical borders, as well as from the Ocean front, leading the Mirages and the JFT's naval support squadrons.
It seems as this is the game plan and which is why more ZDK's weren't ordered as they would be maintaining a rather smaller ocean based area 300KM from the coastline of Pakistan. 1 ZDK covers it, you have three, 1 for backup / maintenance coverage and the third for attrition if any takes place.