How to automap shared mailbox **without** granting Full Access in Office365?

I want to establish a shared mailbox for a project team. I want this mailbox to be auto-mapped into the team members' Outlook profiles. However, I do not want them to have Full Access, so I can still control access permissions on individual folders inside that mailbox - for instance, to hide all the superfluous default folders they won't need, but also to have different folder permissions for project leads and mere stakeholders.

For test purposes I already solved this on our on-premise Exchange Server: Simply entering the DNs of the team members into the shared mailbox's msExchDelegateListLink attribute (via ADSIEdit) does the trick nicely and so far I haven't discovered any downsides to that approach. However, as far as I can tell there is no way to access that attribute (or any attributes for that matter) in an Office365 environment.... or is there?

I feel I must be missing something essential here: Why exactly is auto-mapping tied to Full Access in the first place? Is my use case really that outlandish? Are there other approaches for this that I simply haven't thought of?

Why exactly is auto-mapping tied to Full Access in the first place?

Because that's how it was designed? Only Microsoft can answer that. Perhaps you can ask them.

Is my use case really that outlandish?

Not outlandish, but not the use case that shared mailboxes is intended to fit.

Are there other approaches for this that I simply haven't thought of?

Look into Office 365 Groups, or potentially Sharepoint document libraries. I'm not sure what the "right" solution is, but shared mailboxes isn't it.