Lieutenant Dyester couldn't help but compare the current Khan to the kid from his memories. He still recalled how broken up Khan had been about his actions on Istrone. Many soldiers would have never recovered, but Lieutenant Dyester now knew that Khan didn't have that option.
The nightmares had forced Khan to stride forward. His curse had pushed him past the breaking point multiple times, worsening his already damaged psyche. He was basically compelled to overcome every tragedy that befell his life, and the price couldn't have been low.
Lieutenant Dyester was surprised Khan didn't turn into a complete psychopath. Anyone would have gone crazy or given up on life after experiencing a fraction of what he had faced, and for good reason. Both paths were completely understandable and earned.