Symfony provides a relatively small piece of the puzzle. Its biggest contribution: the gapi services (and other remote APIs) are configured with server-to-server service account access. Sym3 provides an endpoint that returns a svc acct access token that's - in turn - used by Ng2 to authorize the remote services.
While the huge majority of BI data comes from 3rd-party sources, some pieces require ad-hoc sources - this is largely where Mongo comes into play. Views such as "Activity Log" need on-the-fly recordkeeping that's best manually entered; considering that fetching from a task manager API will paint an overwhelming or inaccurate picture of the month's activity.