Huge is relative, but Astrum was not the only meaningful realm in the area.
Everguard had from Eidulb to Valkyrja, so 4 potential duchies, for example, and was fairly strong during its time.
But my point wasn't that there was many huge realms over the years there, but that there were never really multiple realms there. I can only recall it happening in the very early days, Everguard quickly dislodging Caerwyn's initial colonization of Eidulb and pushing them to Golden Farrow.
As for Barca, it was tiny for all but a tiny fraction of its history.