That's a valid and interesting question to ask and study, but I don't think it's relevant to the decision of whether it should be illegal.
I’m not convinced that it would be, but it’s an interesting hypothesis.
I don't think violent video games should be banned, whether they increase or decrease IRL violence (I personally suspect they don't have a significant effect either way). And I don't think "simulated CSAM" (where no actual minors were involved in any part of the creation) should be banned on that basis either (though I don't know enough to guess whether it would tend to increase or decrease actual violations).