ben on How to use external users in SharePoint Online (with a cost-free Azure Active Directory)

Can you not add the Security Group specifically to a sharepoint group? I'd rather manage all external users and group in the AAD portal than in both the AAD and Sharepoint groups. e.g. if you create a sharepoint "ext-company1" group and add the AAD security group "co1", and add "user1" to "co1", then you wouldn't need to mess with the sharepoint group anymore and just maintain membership in AAD on the "ext-company1" group. I'm not seeing where SPO will allow you to add users/groups from the 'new' directory created.