Slow mail import of large mailboxes from Apple Mail / GMail - or how do you do it?

I think I’m running into the same issues. I’m trying to run an “Archive Mailbox” on my Gmail account with around 47,000 messages (Mail.app says there are nearly 76,000 messages, but I’m guessing that’s a difference in how they’re counting threads vs. individual messages.


ScreenShot 2021-01-28 at 09.54.04@2x

I clicked “Archive Mailbox” with my Gmail account selected and it’s been running just fine—no crashes or anything—but it’s been running for around 12 hours now, and it’s showing an increasingly higher time remaining, currently sitting at 19 hours.

Is this to be expected? I can be patient, I just wasn’t sure if that’s about what I should expect when importing large mailboxes like this one. Or should I try some of those steps above, and move things to my local machine first, then try again?