This is a late reply, but thanks for your input. I'll look into them further. What interests me is your replacing Dovecot + Sieve with your MUA; I'll have to see if I want to do that or not.
No worries. For some time, before fully transitioning to Notmuch as a MUA, I was running Gnus with just Notmuch (using nnir notmuch search backend). So no Dovecot or Sieve. A pure Maildir.
I'm not sure whether you'd loose any feature like this, I don't think I did. But perhaps it's much simpler and quicker to switch to Notmuch for Emacs.
I find Notmuch + mbsync more satisfying because of efficiency and simplicity. It's a serverless setup, config files are small, and it's very quick.
Both Notmuch and Mu4e have good Org integration, so if you want to explore that route it shouldn't be a show-stopper.