After reading your original post on the problems with this player, I think he's justified in being a bit salty, and in claiming that he was "singled out"--because he was singled out.

In the previous thread, I didn't see a single person saying "just ban his character and force him to re-roll". Because that's only one step below the nuclear option of kicking a player out entirely, and it's an unreasonable reaction to the issue of "this character is a little too powerful".

Look at this from his perspective: he ostensibly put a lot of thought into creating his previous character, and rolled it completely by the book. As far as you've shared, he didn't attempt any homebrew fucketry.

He built a character that was good at exactly one thing: having a high AC. You didn't like that, and didn't accept any of the numerous suggestions of how to adapt to it, so you slapped him with Rule 0: "Because I Said So". Even putting a ban on multiclassing and allowing him to just re-work the character and replace his multiclass levels would've been a better solution, because it would've been a rule everyone had to follow.

And all that multiclassing he was planning on doing would just prevent him from ever getting an ASI or feat.

TL;DR: Jeff is going to be a problem because he's justifiably salty after you _were a problem for _him. Of course he's going to send you his level 20 character for approval--you nuked his previous character out of the blue, even though it was 100% by the book. He has no frame of reference for what you find unacceptable, and he probably doesn't want to invest in creating another character that his DM will find "problematic" and just nuke again.

And I'm not just saying this because we're both apparently fans of American Gods.