Heres how sin CC breaks work. In order to combo em down, you need to negate them in succession. They can roll out of a knockdown or daze once every 8 seconds. Every 36 seconds, they can roll out of a stun. They also have flower, which allows them to teleport to flower during any CC. As a des, ideally you would force the sin to fight near enough to his flower that you can easily get to him after he uses it to break a CC. Use your skill that dazes + draws opponent within 8 meters (I forgot the name, but it functions the same as BD's form 2 V skill) to break his stealth - when he rolls out of that daze, then you use your throw axe skill to bring them back to you (be careful not to let the sin counter throw axe). This will sit him under you during daze, at which point you can pop fury and start smashing away. This will bait his flower teleport. After the teleport, wait about 1 second, and then use your leap to stun him. He will likely roll out of this stun, but your throw axe should be up by then - use it again, and finish him off with a grab > aerial combo.
There's tons of ways to beat sins, and what I suggested is only one. I don't even play des, so it may not be completely accurate, but the gist remains the same - bait his defensive cooldowns by using your CCs in succession, and eventually he won't be able to roll out of . Just be careful not to waste your CCs on a counter or his SS/E/Q. As for avoiding his poison and slows, you would have to time your spin to deflect, or SS if that's not possible. His teleport swap can't be deflected with spin, the only way to avoid it is to predict when it's coming and SS or your invulnerability skill (dunno the name of it, it leads into your aerial knockup). Most sins open with either teleport or sneak attack. If they open with sneak attack, if you time your roll perfectly, you can avoid his aerial knockup, which will save you a lot of trouble.
Sins are actually punished quite heavily for mistakes, if he gets out of a CC with flower/counter/whatever, that isn't really a mistake. Just gotta learn how to bait their defensives while avoiding their highly predictable openers. Spin out or SS the poison shurikens, and shield up as he breaks stealth to plant flower, you'll catch him with no way of restealthing and pentaslash goes through counter.
Des with perseverance build is pretty hard to stun down, but they're one of the easiest classes to counter their opening. Throw is slow and predictable enough that you can SS it, and jump can be dodge by just holding q/e. Red spin can be lethal if they catch you with SS down, so if you have to use SS to avoid something, make sure you don't land near the des, or if you do, land a CC to buy you the 8 seconds you need for CD. Instead of going for stun chains against des (aside from punishing huge mistakes), go for aerial combos. Spec blitzblade to break defense and you can negate their healing on shield (and usually catch em by surprise with a followup raid/pentaslash).
If they're down on throw/jump CDs and spinning to avoid, hug them, spam spin, and trip with 1 - you'll regen chi off deflects, and trip goes through spin (but not the .5sec deflect window). Know how to tech-chase them - aerial drop and break blade knockback can be knocked back in the air with Cheap BNS Gold if performed before the counter goes up, and roll can be chased with raid or Moonlight blade form2. A good combo is groggy speced grab>drain to bait the roll, then moonlightblade to put back in daze for aerial. Beating des as BD is all about being patient, knowing how to avoid their damage,tech chasing, and chi draining. Bonus points if you can force them to burn perseverance to break out of a CC at an inopportune time, for example with your shield and SS up.