The F-6C don’t have a radar while the Mig-19PT have
AIM-9Ps?
Radar performance (or even total lack of radar) means basically nothing. Neither airframe has SARH nor is SARH combat even really a thing at this BR and whilst its incredibly useful in ASB for finding anyone at higher alts, in ARB, thanks to markers, radars at this BR range are largely just extra weight. In aircraft like the Lightning F6 at a similar BR, I usually just have it switched off unless I specifically want to scan for something up high.
What is different is the available A2A missiles. This being Mig-19PT with R-3S (essentially the soviet equivalent to the Aim-9B) and the F-6C armed with Aim-9P a notable upgrade over the R-3S.
F-6C also appears to have a higher climb rate and better turn time.
So TLDR, F-6C is a direct upgrade over the Mig-19PT.