When someone is banned, their posts are automatically deleted, it’s not some crazy admin obsession to ‘purge your entire history’.

Nope. That's not how it worked at the time. I even still have screenshots of being able to see banned users posts still there from around this time. My comments specifically showed "removed by mod". I just checked and I can still see a post by an alt I made shortly after being banned (which was then also banned shortly after). So no, banned users did not have their posts automatically deleted.

Proof right here even.

This story does appear to be “an admin abused their power to ban me, then that admin got banned for being caught abusing their power”. Which is not uncommon in online communities.

That is not remotely what happened. The person in question continued to be a mod for some time. Their eventual banning had nothing to do with what happened to me or others.

There were multiple mods and admins acting this way around this timeframe against many users on the site, so they'd all have had to ban themselves for the same behaviour.

Edit: Actually, now checking again, and the mods account in question doesn't even have the banned indicator, so I think they may have just deleted their account.