This is why Sudden Demise is useless for PvP and should not be a talent in the last row for the spec.
In PvE Sudden Demise uses your bleed damage to kill targets below 35% health, in PvP it’s only 10%.
For reference I am using my own rogue as a default with his health being 750k in 10.2 in PvP.
10% of 750k = 75k damage. Remember, this damage will only trigger ONCE per player you fight, and only if you actually get them low enough to kill the player.
What is 75k damage to the spec overall? Well, let me give you some more numbers.
A single garrote at my health/gear is over 100k damage.
A single rupture is over 100k damage.
A single Envenom crit is over 80k damage (without any other buffs than it being a crit)
How much worse can it get? Lets take a look at Sepsis, a talent that is two talent rows above Sudden Demise that is generally not used in PvP because it’s considered not that good.
Sepsis does about 100k damage to a player in form of a Damage over time. Sepsis also gives you access to a stealth ability when used (for example garrote silence or cheap shot can be used, or ambush)
If the player survives Sepsis, they receive 55k damage just for not getting killed, than you get another stealth abilities use AND the cooldown of the ability is reduced by 30 seconds.
Sepsis literally does almost as much damage as Sudden Demise just by the player not getting killed by it.
This all being said, I believe without a doubt that Sudden Demise needs to be changed/fixed for PvP, it should not be this terrible.