The only thing I've found is to run the accounts cull tootctl command followed by deleting the folder and then running accounts --refresh all tootctl command and wait for it to download several gigabytes of images all over again in the hopes it won't be as large as it was before. I gained back 2GB that way. Yay, but it's still stupidly large for no reason whatsoever.
I think I might see about querying the accounts table on the database for ones that haven't been seen by me in <insert time here> and then just removing them. If I ever encounter the user again it'd be gone. The cull command obviously doesn't catch them all because if it did I wouldn't have randomly picked that one I hadn't seen since last year.