I am inclined to believe Dalinar's conclusion that it is a young Nohadon, before the title, before the kingdom and before the book. It makes the most sense with the available evidence.
I feel like both Derethil and the Sunmaker were more recent than Nohadon. I don't have anything to cite about Derethil's timeframe. But, if I am remembering correctly and the Sunmaker was the guy who reformed the Vorin church, then he was alive a very long time after the last Desolation.
Although I do agree, Zenous, that Derethil is probably important.