My thing is all of those have some clear weakness to their abilities. Morg and Anivia are slow as balls. Syndra needs a bull. Vel'Koz has a clear tell. Ahri, Lux and Xerath are a little trickery but they are all fairly short overall. Veigar's E varies but it's probably the strongest one there. I think if we want to compare pick, I would compare it too Elise's cocoon. Those two are comparable due to their raw power (2 seconds of stuns), the following burst from the champions and what matters most, the speed and visibility.
Seriously, Zoe's E can be hard to see when you are close, can be hard to tell you even have been hit by it to be honest, and it moves REALLY fast. At a standard cast range, this sleep can be fairly difficult to react to and when it hits, it has a massive effect. For at least 1 second, a person is just out of a fight. Most people will look to find some cover because they know how deadly this effect is. That's before you even get into the CC part. Than you have 2 seconds of hard CC that massively debuffs you. So now you have a long CC effect that is fast and comes with a debuff.
That's before we even get into the range and the extra effect of it becoming a trap. Zoe can possibly effect a lane she is only somewhat close to making her has a lot more map pressure than you may think. Seriously, Zoe could be at dragon and throw a trap almost all the way to bot lane. This has some insane power someone can use and the effect is so powerful it hurts.
Zoe's E is to Zoe what Ardent was to Enchanters. It is the champion.