Shallow statistics are never going to replace empathy* when it comes to sound policy making.
That study does show that banning content within a forum means that you will get less of that content on that forum. A useful but not entirely surprising result. As a Reddit user, I'm glad that the site has less of such content.
It does not prove that censorship reduces "radicalization" (whatever that is). As the study says, many of those users just moved their content to Voat.
*By which I mean cognitive empathy: the capacity to infer the motivational states of other people and anticipate their actions.