I see no reason why PM of a country, going on an official visit to a foreign country, cannot either charter or have a dedicated aircraft for this purpose.
IK is not going on a joy ride, nor is he bring an entourage of sycophants with him. The whole reason why important people fly privately is not to waste time. Imagine seeing the PM of Pakistan waiting in a transit lounge waiting for his next flight. Yes, the optics looks good from a PR perspective, but it's a waste of time. And we all know that time is money.