I think an important question to ask is what the mid term development cycle for the J10C? I would imagine PAF is privy to that roadmap. This might include more advanced munitions, higher load with enhanced engines, more downstream tech integration from China broader development efforts. We could see a decent J10C which could give us a near term answer to address regional threats.I would've liked that approach, but I can see where the PAF is coming from.
Basically, any NGFA investment would be a big risk and massive use of funds. You can't park all of your eggs in that one basket, no matter how good it sounds in theory. You need a "control" to fall back on in case the flagship program (NGFA) hits a snag, and it will hit a few snags.
So the question we have to ask is, "what is a good enough control?" Maybe the FC-31 might have been the ideal control, but it's not a factor (still in development) and will likely be costly. The JF-17 is available and is lower cost, but it may not be enough to handle the threats of the 2020s and early 2030s.
This basically leaves us with the J-10CE. From the PAF's standpoint, the J-10CE is probably good enough to support its needs for the 2020s/early 2030s, and it's available at an acceptable cost. So, if things go sideways with NGFA, the PAF could keep adding more J-10CEs without necessarily compromising the future NGFA procurement.
There might even be some other factors, such as the possibility of using the WS-10 in the TFX and building engine commonality between the two future mainstay fighters.
Moreover, Pakistan can only support the development (or co-development) of one fighter, but it needs both heavyweight and medium-weight jets. So, one of these must come off-the-shelf, and the J-10CE met the ASR for the near- and long-run.