I think Arthas would have sacked silvermoon even if he wasnt salty. These factions should be compared before their downfall.
Example NE before the orcs set a foot on shores of kalimdor and before Arthas waltzed to the sunwell. NE ruled from M.t Hyjal to Feralas while BE ruled
current ghostlands and Eversong Woods.
By those standards NE had a larger kingdom and longer lives so they could train and master their way of war longer but BE/HE have waged more wars because they allied with human kingdoms and their wars.
The birthrate of BE surpass the NE but by that timeline NE empire would have more soldiers and combatants to call than the BE. Question comes can the NE overcome the birthrate and training of BE in a war of attrition if they cant overwhelm and have a "Quick" war