If looking for local email, why not a traditional client (thunderbird, claws, even outlook) or the more flexible/cli friendly maildir and notmuch? There are a bunch of front ends, including WebUIs https://notmuchmail.org/frontends/

Is what you're looking for a pretty good fit for how email was originally used? Or am missing something obvious

Actually, that is what I would like, but if I use Thunderbird on my Maildirs (served by Dovecot), the search (particularly in the mail body) is not really feasible. Perhaps there is a search integration for Dovecot that I am not aware of??