JH-7a is covered by J-16 in range, speed and payload indeed. Replacement of JH-7a is more or less booked already with J-16 and J-15 variants.If the capacity allows (or more like regardless of), there should only be one major platform for land-attack/anti-ship-focused missions, not two.
Also, the JH-7/A was born in the era where China finds itself severely lacking in the department of land attack and anti-ship capabilities that doesn't require deploying H-6s every time.
Now, with rapidly growing numbers of J-16s in service and with J-36 + new strike UCAVs arriving in the future, there is no longer any need for a new "JH" fighter-bomber type of warplane.
Only thing needed is a longer range platform to replace H-6 multiple missions profiles. H-20 will probably fill some of these missions profiles but I'm pretty sure there's a gap to fulfill with a new airframe. I cannot see them replacing all H-6 workhorses with 4 engines stealth bomber. When a clear H-20 design will emerge we will be able to sort out things.