Small test in video with my NS :
100% cast, without haste :
with haste 2 lvl 2
In both case it take 140s to fire 100 deadly light. IF haste 2 lvl worked properly, it should take 54s...
With haste, we can see the animation is faster, but the skill didn't fire after the animation, it fire after another animation cycle start, so it's impossible for NS to reduce the time between 2 attack skill, Deadly light can't be fired more than once every 1.4s
It's the case for EVERY NS attack skill, none of them work properly with haste.