It would seem to me that the victimization of the is only PART of the crime. It's also a breech of socially accepted moral norm. Which is why the crime isn't simply classified as sexual assault. So fake child porn escapes the victimization-of-a-child criticism. But still runs afoul of the moral code we all accept as part of society 

 By analogy plagiarism is a violation SEPARATE from the fact that it's a violation against the originator of thw content

At least this is how I interpret it..... so I would argue that deepfake child porn should still be illegal insomuch as it's still child porn - regardless of the "realness" of the child