1: We're leaving jamming out of this for the moment, and only talking about the idea of hitting a moving target with a ballistic missile.
2: I'm not sure what your point is. ABM tracking is indeed done by other platforms. But AShBM's tracking will be done by other platforms until the terminal phase too. Seeing as ABM supposedly doesn't have to worry about its datalink being jammed shouldn't the same logic work for AShBM lol...
3: But AShBM won't be searching the entire ocean will it? The ocean might be 1000x1000 squares large, but offboard guidance/datalink will send it to the 10x10 square where the CVBG is. Then it will be up to the terminal seeker to look for the 1x1 square large CVN.
4: What's stopping C4ISTAR loading "new info" into the RV during terminal phase? For instance, instead of targeting the 100k ton CVN with fighters, command the RV to go for the 40k ton LHA laden with marines instead?
My point wasn't that ABM and AShBM were directly comparable, but rather that saying "it's not been demonstrated to hit a moving target with an IRBM!!!111one!" would be far more credible if ABM hadn't demonstrated hitting a ballistic missile with what is effectively another ballistic missile. Like I said, ABM is like hitting a bullet with a bullet. So AShBM will be like hitting a barn with a bullet.
Btw I don't think DF-21A has an active seeker (100-300m cep). It is used for nuclear strike anyway. It is DF-21C which was said to first field an active seeker -- it has a conventional warhead meant for targetting bases and high value assets etc (30-40m cep)