Raj'Dur Plateaus, Takish Badlands, and Sandstone Delta are all on the same continent as Sinking Sands and Pillars of Flame. The zones added in the Desert of Flames expansion only cover the north half of the continent of Ro, while the zones added in Renewal of Ro cover the south half of the same continent. Thus, Takish'Hiz is right where it's supposed to be.
As Benj noted, the 'remote island half across Norrath' IS Ro. The upheaval of the shattering moved it 'half across Norrath'. You'd have to go through all of the lore back to the begging of DoF to get to the full scale of the story, but that continent is the entirety of Ro.
