[dreadnaut]

> My complaint is it should store each email in its own file

Thunderbird supports one-file-per-email (Maildir) accounts, see settings. It's still marked as "experimental" because of some edge cases, but I have not encountered issues in many years, and it makes for a snappier experience.

- https://support.mozilla.org/en-US/kb/maildir-thunderbird

> There's still no way to backup my account settings.

Import / Export settings has ben around for a few versions:

- https://support.mozilla.org/en-US/kb/thunderbird-export