If they seem foreign to the setting, it's because they are. Dargonborn as we know them were a fairly recent addition to the setting (4th edition) IIRC WOTC added them just because it seemed to them like something that would be popular (riding the popularity of Dragonlance's Draconians, no doubt) So they were added through the whole Spellplague thing in 4th edition that was basically a reboot of the setting. They never really had a huge amount of lore behind them or integration into the setting, and being perhaps the biggest standout of 4e that wasn't retconned with the second sundering makes them stick out like a bit of a sore thumb in the setting IMHO.
