SMTP/IMAP v Gmail API

We've been working though the Google OAuth process without much luck. Our product uses many restricted scopes which is making it very difficult to on board anyone outside our team without the OAuth approval. We've explored the option of publishing in g suite marketplace as an add on but restricting access to g suite users only (but g suite admins need to allow access from their login). But we can't be certain with how Google would view products like ours moving forward.

We're now contemplating converting to SMTP/IMAP integration instead of google APIs. Looking for any feedback on the comparisons.

Thanks!