Sins have no cooldowns that defend against nontech/force without aid of the RNG. NM (and HM operations chief) as a sin is literally "roll 1d6, if you get a 1, you die even at full health".
Overcharge saber... It increases DR by 25% aka 60.53% total DR for 15 seconds in full underworld. Put that with a exotech absorb adrenal and you have 15 seconds of 70% DR! So what exactly are you talking about when you say sin don't have any cooldowns against nontech/force without the aid of the RNG? I'm pretty sure DR is static.
Also the math has been done on Operator cheif, he doesn't one shot you in HM, he can kill a nonshielded sin who is below ~75-80% in one hit for 16 man HM. NiM will need a cooldown, but this is true for all tanking classes now.