Another option (which is already in the game script with the saving throw calculations) is just make all skills debuffs have duration based on rank in the skill-type (and talent bonuses) that stack in duration and then % of that duration (rounded by +/- 0.25) is applied proportionally to % of current shield you did in damage. If a 600 hit with 2 turn knockdown hits a 2k shield, there is no knockdown, but if you had torturer, you would get a 1 turn knockdown since 3-70%=0.9 thus rounded to 1.
Soft cc and dot debuffs would have higher base turn count, hard cc lower, if warm>burning would be resisted, it would still roll for increased duration of warm then (same for chill>freeze), but poison and non-ground oil would need rolls to explode (or wet to freeze).
Taunt, Madness and Charmed success rate could even be based on more flavor based/classic D&D thing like caster vs targets Constitution, Memory and Wits respectively with small bonus given by Ret, Leadership and Perseverance (again respectively).
Perseverance could then also be a universal on hard cc proc for the armour restores AND be a nice boss stat (do you cc and prolong the fight a bit depending on how high it is vs take a round of meteors to the face, but not "heal" the boss).
Torturer doesn't do what you think it does. It only applies to DAMAGE status effects, meaning things like burning, bleeding, poison etc. I didn't notice it being applied to rupture tendons either, so it seems it only works on standard DOT effects (probably not Shackles of Pain either).
Nearly all CC effects in the game last only one turn. There are a couple of two turn effects, but they are very rare (love grenade is all I can think of). Thing is, they don't really HAVE to last more than one turn. You just re-apply CC any time during the round and perma-CC from there. Not very many enemies have Perseverance, and those that do don't normally have too much of it.