FWIW, I've almost never seen this argument made by people who aren't secretly or openly supporting those who are banned (you being the exception here).

I believe there's quite a bit of data now that shows that deplatforming tends to work. I have forgotten all the names, but someone named "Milo" seems relevant, and wasn't Alex Jones also banned from somewhere and lost a lot of influence since?

And those are the cases where bans would tend to fail, i. e. people that had years to grow a loyal fan base, collect names & emails, etc. If it works in those cases, it should be extremely powerful when being used a bit more proactive. Anybody watching /r/thed... would have known it's toxic two weeks in, before it had time to spiral entirely out of control.