There is a difference between the inherent capability that an aircraft offers and the way it is employed in a conflict. The former determines the range of missions that an aircraft can conduct, whereas the latter is dependent on the aircraft's inherent capability as well as the makeup of one's own force, the disposition of the enemy, the maturity of the platform, and other strategic and operational variables specific to each conflict scenario.
If the PLA had to go to war with only a brigade of J-20s in service against an opposing force with a large fleet of both 5th and 4th gen fighters, you can bet that PLAAF would use their J-20s in the most cost effective way possible. That would likely include targeting opposing force multipliers at first, and then to operate in a manner to indirectly support 4th gen fighters with its superior sensors and SA.
But if the PLA went to war in ten years with hundreds of J-20s in service against an opposing air force with a fleet of mostly 4th gen fighters and only a hundred of their own stealth fighters in service, then chances are J-20s will be used much more boldly, though naturally it would still involve targeting force multipliers as well.
In fact, I would expect in the opening phases of any high tech air war, that each side with stealth fighters will try to go after each other's force multipliers, and that isn't unique to the PLA.