That's all well and good, Cure, if the Forsaken actually did sit there and brood. But they didn't. They actively designed a plague that, when used, would wipe out both the Scourge and the living. If you'll take note, the latter of those not only includes most of the Forsaken's enemies, but all of their allies. They are a heavily militarized society. They just make up their possible lack of numbers with a heavy investment in WMDs. On top of all of that, in Cataclysm the Forsaken are one of the single largest conventional military forces in the northern half of the Eastern Kingdoms, if not the largest. Gilneas lost a large portion of their military to the civil war, curse, and Forsaken invasion. The Ebon Blade is largely inactive, either unconcerned with Azeroth's geopolitics or dispersed among the Alliance or Horde. The Blood Elves are still rebuilding. The Argent Crusade is mostly confined to cleaning up in the Plaguelands. Meanwhile, the Forsaken expand with frankly minimal resistance. And this is all after losing the bulk of their military to the aftermath of the Wrath Gate.

As to the Ebon Blade being a more militarized force, they did not march into Icecrown alone, and the times they employ traditional military tactics are few and far between. The Argent Crusade was the blunt military force. The Ebon Blade's tactics were all about subversion. They have you control lesser undead to sow discord among the Scourge ranks and sabotage their machinations. They team up with Alliance and Horde officers to try to compromise the physical structure of Icecrown Citadel. They have you commandeer weapons so they can be used to sow chaos among their enemies. The only times I can recall the Ebon Blade acting as conventional soldiers and not special forces since Lights Hope is Tirion's Gambit and the final quests in the Fleshwerks, both of which happen at the end of quest chains where Death Knights deploy the players to act as special forces.