J-6 in suicide drone just with their mass and speed would bring quite a level of destruction. Strapped with half a ton bomb you need to destroy them asap. A wave of hundred of these and most Taiwan SAM launchers need reload but making them fly all at the same time is more troublesome.
As large Supersonic jets, they might be more useful and very valuable as large UCAV drones to be used as CAS bomb trucks or ISR drones instead of just using them as a suicide drone against Air Defense. They r cheap to operate and maintain I assume. It might be cheaper to just use MLRS rockets to oversaturate Taiwan AD.
Moreover, in a WW3, China might lose its frontline planes quickly. War of Attrition requires high production numbers but also a strong storage of older planes, ships, tanks and everything. J-7, J-6 might become the backup fighters for Air Defense.