I'm not an expert on terrorism in particular. However, I will note, from the empirical research that I've seen, that there seems to not be a clearly established causal link between removing such content from social media platforms and public safety. There are a few reasons for that. The first is the reason you mentioned, which is that these users might go into darker enclaves on the web that are greater echo chambers. In addition, it is more difficult for law enforcement to monitor some other regions of the Internet.
Finally, one of the issues that has been raised is the idea that if you kick users off of these platforms inaccurately, it might disenfranchise and marginalize those communities, which could lead to violence as well.