For all those datalink related issues you might consult F-35's level 4 update. Which drastically improves it's datalink capabilities and also includes costly hardware upgrades. Their details are more public than the Chinese equipment. And PAF have removed some unnecessary components to make it more cost effective for them. Yes when 5th gen fighters would come almost a decade later, these brand new fighters would be going through their 1st overhaul so can be refitted with datalink of that age.
The latest upgrades in F-35 can let them communicate with multiple assets at a time with directed communication beams which are harder to intercept and jam. And they can literally receive and relay HD video feeds to/from different sources and it can't be done in current tech of 2mbps link16. So 5th gen fighters have situational awareness, data fusion and data transfer rates a lot more higher than any 4th gen fighter could even handle it. This requires processors with multiple times more processing power and related equipment.
And it's like buying an expensive spacesuit but there isn't any rocket available to you to actually go into the space
. That's the whole purpose of modular system. You can upgrade as and when required and luckily PAC is skilled enough to install some communication modules in a jet, they wouldn't have to go to Canada to do that.