I do agree with Winged Serpent having a bigger cooldown, but not with Snake Dancer's. Blind, knockdown and rear attacks already seal the deal with that trait, and things like DoTs like poison tends to remove one stack at the beginning of the fight. That'll leave them with one 'invicibility' only and be vulnerable for the rest of the round, which, mind you, Snake Dancer's users tend to be really squishy.
Any DoTs taking away stacks of snake dancer is purely a bug and should be exempt from basing judgement on the Snake Dancer skill itself, but I believe that DoT thing to be visual effect only, the stacks in the corner for Cobra have always been visually buggy anyways.
The lower your hit chance is, the more drastically that double check actually lowers your hit chance, snake dancer serves as a huge annoyance to archers and gunners especially, to make the argument 'but they have range' is actually their biggest downfall when it comes to this passive, and thats because of the line of sight cone
which makes it near impossible for them to travel out of the farther away they are, which Cobra has easy access to kiting with winged serpent.
If you have a 20% hit chance on somebody, lets say because they proc'd Yomidori or what not, you don't have a 1 in 5 shot of hitting them anymore, you have a 1 in 5 shot of hitting them on top of another 1 in 5 shot (And this is assuming the evasion proc for Cobra doesn't use current evasion rules, which is docking 10% of your total hit) which would turn out to be an effective 6.25% hit chance, or almost a 1 in 20 hit chance.
Its not just melee duelists who can very easily veer around an opponent who get impacted by this.