Yes, because FC-31 is an inferior product otherwise.
The FC-31 doesn't bring new capability.
F-35 has avionics that are a generation ahead of F-22. Not only is that not the case for FC-31, the FC-31 would likely have worse avionics compare to J-20. SAC has a habit of choosing suppliers only within AVIC, but these suppliers are known to be inferior to suppliers outside of AVIC.
While I really like the FC-31, and it looks like a mini Raptor, which I think is great, like the Eng, I really don't see this bird bringing anything new, other than a smaller lighter airframe that might eventually make a nice little Navy bird, and might be a great fighter to fly off the carrier. I know the Eng is a die hard Chengdu Man! and will disagree with me on this, but that's the only real hope I have for little chick.