J-8II is still consider more valuable than old J-7.. It got a bigger nose which radar continuous upgrade is possible to meet future demand.
It has much much longer leg than J-7 with its long frame body, more hard points. More range and hard point plus bigger payload means its able to handle the multi-role task of ground strike.
There is nothing bad about J-8 compare to J-7 except ONE THING. It cant dogfight like a J-7G.