Its not suprising if the Nightborne feel more a kin with the Sin'Dorei. They did not give up on magic either, even after losing their source and fell victim to a similar decay. They also split up into two groups with one part falling to the Legion out of hunger...Funny enough in both cases the leader they looked up to joined the Legion here as well. The difference being that this split between the current Bloodelves and Kael'Thas' group happened before they were opposing factions, which allowed the Bloodelves to rebuild on their own. Silvermoon was devestated but... they still had it after all to start over and had to take it back from what was left of the scourge, not from their own brothers and sisters.