Except this core does not exist.
There are no (kinda) "fedi routers" that forward all messages from one edge to the other.
All fedi instances are edge routers, instead.
The picture that fits best is that of the decentralized diagram.
To claim anything else is a confusion of layers. The human to human addressing layer is not very interested in the shape of the interface addressing underlay, but the shape of its own connections matters.
In terms of what Baran was talking...