I think Zan Kir will be overwhelming.
Crashing Wave(Q): Its large cone make it easy to land at melee range. While its damage is low, especially its base damage, its very low cooldown and ministun will make it very good at disrupting others. With only 25% CDR and max rank you can use this every 3 seconds! One thing I noticed is that the animation and targeting cone don't match. The animation goes farther in front of Zan-Kir but does not reach the corners on the sides.
The passive is weak and irrelevent. At max rank and fully stacked it gives 18 weapon damage while a single Attribute point give you 7. Even Augments give you more than that! The passive has negligible impact and might as well be removed or reworked.
I'd change it to synergize with the Active part: increase the base cooldown of the skill but reduce it by 10% per stack. Or simply increase the damage of the active by 10% per stack. Or make it pull enemies only if ZK has full stacks. (Each of these remove the stack after the skill use).
1000 strikes (W): usable as a speed boost, a teamfight skill, a waveclear tool or a Stamina recovery. It does lower damage to a single target than autoattacks but lets you move to chase him. I'm not sure how the Armor buff and Stamina works with Units: if used against Cyborgs, will hitting the 15 little soldiers that teleport on you give you 30 Stamina and 15 Armor stacks per hit? Or does it only trigger once per damage wave (twice per second) capping it at 20 Stamina and 10 Armor stacks? Also, how long do these stacks last? Do they drop at the end of the ability?
Double Vault (E): a very good gap closer and escape. It reminds me of Radiant Dash from Karazim in HotS. I'm annoyed that the range scales dramaticly with ranks, with more than 50% increase from rank 1 to 5. At rank 5 its a step short of being able to jump to any Sniper attacking you. I'd link it to a reworked Q passive, increasing its range by 5 per stack and removing the stacks on the 2nd vault.
Also I'm not a fan of being able to jump to Wards, which should be a Vision tool, not a simili-Displacement, in my opinion.
Does the speed bonus for Vaulting to an ally apply to him or yourself, or both?
Duel of Fates (R): A targeted lockdown. the root is long enough to land a Q at max range, but you should probably just walk and keep Q for when the slow starts to expire for maximum annoyingness/lockdown. It can be used both to engage or disengage, You can also make plays with it, dueling a secondary target to stun and move your main target. Can it target "enemy" Units and Creeps?
Overall I think ZK will be overwhelming because of its very disruptive Q, his powerful R and his high mobility. That is, if he builds tanky to survive the fights.
Edit: corrected the error pointed out by @Strapon. Thanks!