While I second most of your points, for me proper navigation and management for the directory tree is way more important than global full-text search, which I can take or leave.
I struggled with the Gmail flow for over a decade until I finally migrated to a self-hosted setup the other year. Finally feel on top of my inbox control for the first time.
It's not about "being stuck in the 90s" (paraphrasing), some minds just prefer hierarchies. Search-based is likewise a subjective preference and not objectively more user-friendly, regardless of how fashionable it is.
That's also valid for me, I auto-refile most of my "recurrent" mails via MailDrop, but most users are piler not filer, and even hardcore filers still need full-text search here and there... Let's say you look for a mail from a friend "a bit of time ago" (no certain date, many messages) about something. You recall some words in it, but your friend is not polite in mail netiquette so subjects are really bad, resorting to FTS is the simplest option. Having tags for casually mark messages with keywords to recall or group them in different ways is also useful because sometimes some messages belong to a certain maildir, but they might be meaningful together with other messages belonging to other maildirs.
Beside that classic IMAP search is HORRENDOUSLY limited and integrated search barely works, we have to deal with html emails, search inside docs attachments, have mails with (sigh) external contents, need full-text search results filtering by date, attachments of a certain kind, size etc etc etc...
We have seen the power of Google Search, we do have FLOSS maildir indexers who give them to us locally... Not having it in 2022 is honestly absurd IMVHO...
I struggled with the Gmail flow for over a decade until I finally migrated to a self-hosted setup the other year. Finally feel on top of my inbox control for the first time.
It's not about "being stuck in the 90s" (paraphrasing), some minds just prefer hierarchies. Search-based is likewise a subjective preference and not objectively more user-friendly, regardless of how fashionable it is.