I think, when people talk about how the son of the survivor can be a Dunyain who feels, they forget that all Dunyain can feel. Moenghus admits as much; Kellhus, in The Great Ordeal, seems to show genuine care for Esmenet. The survivor himself chooses a defective child because it is his son. So I don't think the child is different in that regard; he just isn't as well educated in the Dunyain Doctrine as the rest of them were.
Another interesting thing to note is that the Anasurimbor seem to be best Dunyain. Child Kellhus, in his flashbacks, seems smarter than the rest. And Moenghus calls for his son for his plan, rather than any other Dunyain, and he isn't exactly the sort that'd do that out of sentiment.