What are you ignoring? Ambush numbers for all levels below end game. A rogue at level 10 are 1 shooting level 19s, the same goes for almost any bracket.
How can you fix this? For the first time ever, you have the ability to do it. Since you buy the skill once and it scales with you as you level, You need to nerf this ability at lower levels by reducing its overall damage and slowly increase the numbers as they level to comprehend to the average life of characters at that level, then as they continue to level and once they get to the point they don't do 100% life bar damage: scale their damage to end game then. I think that happens around level 70 which most players have the Def. CD's and Resilience really takes part in the game.
Sub Rogues deal 25% extra damage with their Ambush & 25% more Ability from Sinister Calling.
Next, Sub Rogues get Improve Ambush 3/3 talent in tier 1 which increases its crit chance by 60% and it's damage by 15%.
Recap: 40% more damage, 60% higher crit. Rogues stack Agility and a normal rogue through their entire lifetime have around 20-25% crit normal, that means their Ambush has almost 80-90% chance to crit every time.
Good Luck Blizzard. Hope you can fix this.