I think is Event Horizon is just too strong, it's not even a snare it's a straight up 2.5 second stun in AoE. Thats a significantly stronger CC than Rammus's taunt or Fiddle's fear which is ridiculous considering those champions basically completely revolve around those single target short range CCs.
The .75 second wind up time is virtually nothing when you consider most CC that even comes close to rivaling Event Horizon is usually much harder to pull off. If you drop EH as a follow up to an initiate, they're fked. Even if you just throw down the circle and trap some enemies inside without landing it on the edge, the enemy team will be split and they'll be pressured into engaging a fight on Veigar's terms, or they just leave their front line to die.
The fact that the Veigar rework made it easier for him to stack up AP also just made it much more tempting to get points into E much earlier in the game because he's not as thirsty for damage anymore.