There appears to be essential functionality missing with the current Mailchimp integration that was available within the PieSync integration.
Given that PieSync will no longer exist into 2022, and with this functionality missing on HubSpot, we will no longer be able to deliver the experience that we have been to our clients.
In PieSync, you can sync a HubSpot List over to a Mailchimp Audience list. In HubSpot Data sync, you can not.
One of our workflows:
We've created a customer boolean property know as Is Incident Contact? and we have contacts with this property set to Yes imported into a List on HubSpot called Is Incident Contact.
We have set a requirement for a contact sync to be existing within this list, and if so, they will be synced over to a Mailchimp Audience list known as TrueLayer Incident Communications. We, of course, also sync a lot of data over to this list on Mailchimp also.
It appears as though the current Mailchimp integration simply does not have this integration functionality in mind.