Wouldn't it make more sense that the light Firelink is his vision? Maybe his power is keeping it going, he's the only lord who seems to be there by his own will, Dark Firelink is what "is" whereas the Light Firelink is Ludleth's vision, separated from the world, meanwhile, the real Firelink is dark because the lords abandoned their thrones.
Yeah that's what I meant.
If Ludleth is from Dark Firelink ... Then he was from Lothric...
Dark Firelink Shrine connects to Untended Graves which connects to Garden of the Consumed King which connects to High Wall of Lothric which connects to Lothric Castle...
And you walk from Anor Londo the Irithyll to Farron Keep where Dusk and Elizabeth are, etc. The fact that DFS is connected to Lothric Castle doesn't mean anything.