The only thing I ever had a problem with on veigar
Was the R's scaling of your own AP as well.
MY PERSONAL problem with veigar is that no matter what you did he would succeed in winning his lane.
If you went MR, he still has damage and blows you up. If you went AP, he blows you up harder, if you picked an AD assassin, you were predictable, If you played safe and let him farm, you just let a stacking champ farm.
Honestly, I didn't care much for his AP stacking and the stun, I think the only real change he needed was scaling off of his targets AP as well, there was really no reason for that.