It's worth noting that the PAF may not be planning to put every single AEW&C in the air at any given time. Rather, the large numbers could be a way to keep up coverages when some aircraft go into downtime. So, it could be more about a high coverage intensity rather than coverage reach.
Just my personal opinion, but I think the PAF will try to gradually upgrade most, if not all, of its existing Erieye with the Erieye-ER. Shifting the fleet to the Erieye-ER would enable them to keep all AEW&C further back from the border and, in turn, farther away from potential threats. The upgrades won't happen at once, but gradually with 1-2 aircraft sent to Sweden at a time. That's why ordering a few additional AEW&C (especially Erieye-ERs) is key, helps ensure that the PAF's required coverages are kept as some aircraft go overseas.