Nightblade Ability

Death from the Shadows: Deals 1753 to 1927 death damage. From Stealth. Awards 3 Combo points.

Compared to

Dark Malady: Deals 1143 to 1246 death damage increases damage by 20% for 8 sec. From Stealth. Awards 2 combo points.

Death from the shadows is definitely not an upgrade. You get 20% more damage to your next 8 gcd. Compared to 600 damage. Nightblades are not in a rush to hit 5 combo points. They are in a rush to get 5 gcd combo builders.