The problem with GMail is people are use to keeping all there email in the INBOX! Apple wants INBOX ZERO so that is why Apple email programs have problem with Apple Mail connecting to a Gmail Servers. Plus Google likes changing there email servers all the time.
Really? I have two Gmail accounts with thousands of emails each, and using both for several years.
I never had any issues with either account (using iMAP). The only minor nuisances happened twice when Google decided to ask to enter my password again.