"It's war time" doesn't actually excuse what Jiang Cheng did to Wei Wuxian even when he first strangled him and blamed him for his parents deaths given even he narrated it as such:
"Jiang Cheng pinned him to the ground and snarled at him.
"Why did you have to save Lan Wangji?! Why did you have to meddle when you could’ve stayed out of it?! How many times have I told you not to stir up trouble?! Not to fight?! Do you like playing the hero so much?! Do you see what happens when you play hero?! Huh?! Are you happy now!?
"If Lan Wangji, Jin Zixuan, and the rest die, then so be it! Let them die! What does it matter to us if they die?! What has it got to do with our family?! So why?! Why?!"
"Go die, go and die, all of you, go and die! Die!”
Wei Wuxian’s face was red from suffocation. “Jiang Cheng!”
The hands strangling him suddenly loosened their grip. Jiang Cheng leveled a glare at him, tears tumbling down his cheeks. From deep within his throat escaped the sorrowful, anguished moan of one near death.
"I want my parents. My mom and dad…” he wept.
He asked Wei Wuxian for his father and his mother, but it didn’t matter who he asked.They would never return to him again.
Wei Wuxian wept as well. The two slumped back on the grass and watched each other cry bitter tears.
Deep down, Jiang Cheng knew very well that even if Wei Wuxian had not saved Lan Wangji in the Xuanwu of Slaughter's cave at Mount Muxi, the Wens would have found a reason to come knocking sooner or later. But he couldn’t help but think that had it not been for Wei Wuxian, perhaps it wouldn’t have happened so soon. Perhaps there would’ve still been time to salvage the situation.
That “perhaps” was agonizing. With no outlet to vent them, his remorse and fury consumed him and tore him apart with grief. "
He puts a blame where it does not belong, which should have been Wen Chao, Wang Lingjao and Wen Zhuliu. He however, continues to use Wei Wuxian as the one who made everything go wrong and to hold that grudge against him simply by having existed. Which has always been the core root of Jiang Cheng's problems; If Wei Wuxian didn't exist, his life would have been so much better, despite his issues having been prominent even before Wei Wuxian came to his life.