Kil'jaeden's return to Argus did not go smoothly.
Although Sargeras had not stripped him of his title or power as a Greater Demon Lord, and in theory Kil'jaeden remained the current supreme leader of the Burning Legion, he had suffered terrifyingly severe injuries while receiving the Dark Titan's power and fighting Diakum.
Those wounds could not be healed in a day or two.
Then Sargeras issued the order to "fight to the death," causing Kil'jaeden's conscription order across the Twisting Nether to be carried out to an absurd degree.
By the time the war on Azeroth had ended, the Burning Legion's internal structure had suffered an almost catastrophic blow.
In the latter half of that war, the consecration of Ashbringer from High Heaven had continually been cast upon the children of the world. This meant that every demon slain during the latter half of the war had been burned to ashes and could not be resurrected.
And those demons had happened to be the true elite personally trained by Kil'jaeden over the past twenty thousand years.
In other words, the Dark Titan's final command had directly crippled the Burning Legion's most combat-capable vanguard, while the damage to its command system could only be described as devastating.
From the Conqueror's perspective, the Burning Legion still did not lack the cannon fodder and core troops needed for assaults. But until its command structure recovered, the demons could no longer launch the vicious, swift invasions they once had.
The Legion had lost the ability to wage large-scale war.
Even if its grassroots forces remained, fighting powerful enemies under such circumstances would inevitably devolve into the worst kind of piecemeal reinforcement tactic.
That would be a truly rotten war.
But then again, demons did not care. As long as they had a war to