I'm far from a Gnus guru, so perhaps I'm missing something, but why do you prefer Gnus to Notmuch or Mu4e?
IMHO Notmuch has a very clear MUA model. Plus it's extremely fast and simple. Everything is done via tags. Notmuch never ever touches your email. This is the task of a backend, which has to translate tag changes into Mailbox actions. I do this using a few trivial Bash one-liners, which accommodate for Gmail's unusual IMAP implementation.
Mu4e is more similar to Mutt, as it does touch email directly, allowing you to move emails across folders or delete them. I also found the interface a little bit less snappy than Notmuch.
Gnus has some great ideas, but it's quite slow and the internals are a mess. It needs some serious refactoring.