The main reason I chose Gnus instead of mu4e or notmuch is that I did not want to sync all my mailboxes to local disk. What is perhaps not so well known is that IMAP provides its own server-side search engine. Searching mail with Gnus search queries [1] works really well, and I do not have to manage any overhead to get my mail synchronized, indexed, etc. In other words, everything I need for email is built into Emacs (or outsourced to the IMAP server) - no extra packages/software required.
This. I kinda hate, but still understand, the general offlineimap/notmuch philosophy in this space. I am not in a bunker, I am not optimizing for a situation where I only have internet intermittently. I just don't want to leave emacs if I dont have to and want to be able to be quick and seamless between my code, mailing lists, rss feeds, org mode, and email in general. It was hard won, but I do get this with Gnus now. And yes, love how you can hijack almost all the IMAP/gmail niceties this way with a little bit of work, especially search.
One thing I have done is export the mbox archives of my old gmail accounts and keep them around in Gnus if I happen to need to search through old emails.
[1] https://www.gnu.org/software/emacs/manual/html_node/gnus/Sea...