Annie can flash ult
The fact that you're scared of immobile champion wasting their only real escape.
has an instant stun that is easier to land, does massive AOE damage
I didn't know her Q was massive AoE damage? No she has an ultimate ability that does decent AoE and is easier to land (but doesn't trap them like Veigar's box did, if Veigar missed the stun then his enemy was still confined to a small space with no escape for a couple of seconds) but her stun is not her ult.
In fact Veigars stun was just 1 ability. He used 1 ability to instantly stun you or trap you in a box where you feared being stunned. Annie on the other hand had uses 2-3 of her resources to get that stun off. 1) she gives up her passive 2) she gives up her ult 3) she potentially gives up flash, one of the highest valued skills in the entire game.
Veigar got to choose when to stun you and he didn't have to worry about much else. Annie knows that by using her abilities to waveclear when you have 2 minions at her turret she's going to have to give up that stun she had charged or lose her turret. Yes, Annie can hold her stun to fear you, but remember she can't use any of her offensive abilities while she's zoning you our. She has to rely on her AAs to last hit even with her Q passive, she can't waveclear, she can't easily take blue from her jungler, she's not much help at dragon because she can't spam her spells and keep her stun up at the same time. Veigar's stun was its own ability and didn't interfere with how she played at all.
We could also talk about how banshee's screws her up a lot more than Veigar. If somebody has Banshee's Veigar can hit them with a different ability first. If Annie has stun up and the person jumping on her as Banshees up she cannot under any circumstances stun them. She has to use her stun charge to pop the Banshees then if she has ult she can use all 3 of her other spells and hope her 1st one comes back up to stun you before she dies, or if she doesn't have ult she has to wait for her Q and W to come back up for peel. if you jumped on Veigar he had a fast moving Q and then an instant stun. Even now if you were to jump on Veigar with Banshees he can Q you and then place his box to zone you out.
Veigar's ult could pretty much one shot anybody who wasn't a tank meaning if you got stunned you were dead. In fact a fed Veigar could pretty much 1 shot a person with his Q before the rework. Annie's Q was never going to 1 shot someone. They're different characters and Annie's whole character is based off of her stun and her bear whereas Veigar was based off of unlimited AP stacking and quick burst. He had that instant stun on top of all that. That's why he got changed.
has an instant stun that is easier to land, does massive AOE damage, and can be held to zone for as long as she pleases. Riot if you are going to set a precedent that instant stuns with massive burst to follow are toxic and lack counterplay, you cannot just leave certain champs with the same exact type of kit alone. Why should 
be punished while Annie can flash ult and kill you instantly with her burst while giving her opponent no time to react.
