Double stun, do not forget that part, and that is very easily chained too even with high ping. There is a reason why Ninjas are routinely a source of frustration for every other class on the field, they have an answer to everything and can take advantage of everything, add in an LB that literally laughs at the concept of health (Range certainly doesn't feel like 20 yalms on it either) and it's easily chainable.
That it can't use all these things at once is moot point, they don't need to, because they rarely need to solo anything and if they do, they have an answer for that as well (hide and run away). The nerfs they've been getting hit with do not address the core problems of the class's inherent balance when put in a team environment under the current PvP situation, hence why people find issue with it.
If it was alone, against itself, it'd be fine. As it stands, ninjas risk considerably less than their teammates for greater rewards, I mean heck you can outright win most duels without even knowing what you're even doing. it is simply over-tuned and every patch concerning their balance keeps attacking the wrong part of the problem. Note that I say over-tuned, not overpowered, it does still have mortality meaning you do need a bit of strategy in your tactics, for which I'm personally grateful for because I actually like the Ninja class - just not in PvP in its current state.
So what's the solution? It could be environmental. Ninja is doing its job yes, and they work best when teamed, but who doesn't? I don't believe all of its frustration inducing moments are wholly its own fault, something as simple as diminishing returns on crowd control effects might at least calm attitudes towards it, reliance on purify is ridiculous, it never helps, and especially not against ninja's instant double-tap. But this is just conjecture at this point.