I was under the impression that goblins were spreading quickly. Yorum has many goblin slaves and they are the types to run out into the wild blue yonder. However, if it makes more sense for hain to be more populous still, I can change the wiki to reflect that.
If nothing else, the rate of goblin population growth per individual is certainly higher than hain. Goblins may overtake hain in numbers eventually.
I was not aware that Yorum had any significant quantity of goblin slaves. We haven't (to my knowledge) canonized the spread of sizeable populations of Rovaick far from the Ironhearts (there
are were a lot in Xerxes, but that's basically in the foothills). That said, it makes sense for Rovaick to start spreading outwards (mostly just those with Sularn's Oath, though, since the others are trapped inside the mountains in fear of being attacked by White Giants).
Anyway, enslaving significant quantities of goblins and shipping them to Yorum would be a significant logistical endeavour and probably one with notable societal impact. Doable, but not trivial.
Slaves notwithstanding, I agree that it is likely that goblin populations will at some point overtake that of the other races.
Also,
@Rtron, is the city of Xerxes (or what's left of it) on Galbar or in the Realm of Madness?