This entire topic is predicated on the enemy being stunned possessing no capacity to predict, juke, or otherwise fakeout the Syndra player. Turns out if you're not moving before a gun fires, you can't dodge the bullet.
Syndra's stun combo (Q+E) is mechanically slow to activate compared to some others (Morgana Q, Viktor E, and similar skillshots) because it relies on two separate abilities firing together. If sphere are already on the ground, it is at comparable speed, but relies on a physical object that must have a line draw between Syndra, her sphere, and her target.
W's repositioning of spheres is a powerful mix up tool, but that too is mechanically slow. Long range W's take around a second of flight time before they can be launched for a stun, not only broadcasting position but also giving generous room to escape to a manuevering enemy. Simply running away in a straight line, often a bad idea, is perfectly feasible here because ... Syndra cannot long range snipe people with W. The skill is too slow for that, specifically. In melee combat where this combo is the strongest, however, it gives Syndra a significant secondary tool in protecting herself.
I do agree the new W passive, which allows multi-sphere throws, is too powerful. It overloads her stun combo by removing the necessity of sphere management and positioning, which intrinsically slowed that combo down a fair bit. There's no way to fix that except removing multi-sphere throws as a passive, franky.
Otherwise, for all useful purposes done by skilled Syndra players, her stun combos are mostly trap based. She dictates an area of control and then half relies on enemies screwing up. The other half is forcing her presence closer, which then directly allows for the first half of this equation to work. Pro-active behavior with her stun, compared to something like Morgana, is difficult to do against enemies who are prepared to deal with it.
Flash comboing, and the enemy flashing to sidestep the stun, for instance, would be a near loss situation unless some other factors overrode it.
bind moves at 1200. 
's stun moves over double that and can originate closer to the enemy to start.
