If the author could only communicate better and bring his changes upstream..
I tried to see what do make of his first patch against Emacs 28 that bring threading to Gnus however it was quite hard to rebase/split them up as the original patch was just one big blob.
E.g. he doesn't just add threading to Gnus but also remove or rename variables, e.g. secondary select methods. He doesn't explain changes, he adds unnecessary or rude comments to the commits or code.
I'm also using Gnus with IMAP directly too but connecting to a remote Dovecot on my root server. Fetching takes maybe 1 or 2 seconds at max.
I filter all my mails on my server before hand.