The biggest problem with the J-31 is that they went budget and skipped the EODAS. If they kept the EODAS, the J-31 could have been a nice F-35 clone to offset the F-35's capability.
Pardon, but why should an omitted EODAS - IMO barely useful or necessary in a factory financed demonstrator project - be "the biggest problem", when otherwise no decent engine is available, the PLA itself is at least officially not 100% committed and as such it's future simply insecure?