Those platforms have not, however, been billing themselves as champions of unfettered free speech before handing out arbitrary unexplained bans when their feelings got hurt or they disliked the speech.

That's true, but there's no reason Twitter/X has to stay like that.

Stack Overflow has a pretty good model. It does not remove suspended accounts nor their posts (except those directly related to the suspension). It subtly signals that an account is in suspension by reducing the account's 'reputation' (internet points) to 1 and placing a small notice on the profile, usually stating the reason for the suspension (e.g. suspicious voting etc).