The real reason Veigar is so "OP" right now:
People have apparently no fucking clue how to itemize properly and instead whine about the enemy-ap-scaling on the ult.
Sure, it is kinda crappy design, but there is a way around that as AP champ:
+ 
Veigar rarely builds ANY MR early on, most of them that I see go straight for the AP.
Literally any champion that can scale with these items can screw him in lane:
... and many more. I started playing when midlane mages were all the rage (Season 2) and what came after as the typical rock-paper-scissors like counter for them? Assassins - especially those that can profit from focussing on MPen instead of raw AP.
In his essence Veigar has pretty much the same weaknesses as he had back then - with the exeption that he can no longer insta-stun you and Q is no longer a sure-hit-spell. Get close to him and he's dead.
It's not like this is anything new...