People are complaining about things Veigar could do for many years now.
Wow! his ult oneshot me, the AP champ with 800 AP and 30 magic resist! (his ult use to have a 120% AP ratio) wow! he has over 1k AP! (when has this ever not been a thing) wow! he has a stun! (it use to be instant) omg he does too much damage! (he use to have a 120% AP scaling ult with a https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSsUxhRs22EogWAcUnEygMVGvrn0MZUBWycqbwXQSlseM3zQ40hIGkJXA added to his full combo. he'd literally 100-0 a volibear with nothing but spirit visages in season 2 if he was even the slightest bit popular. trust me, i've 100-0'd full MR tanks before in season 3-4)
lol. and what changed about him? nearly nothing. he was always able to get a fuckton of AP from his Q. now his W is a tiny bit faster and he gets about 100ish more AP per game. 100 AP to veigar and a faster w means nothing if you land your stun.
Also, I said he was a great champion months ago, tried defending him, and everyone disagreed with me. Now froggen plays him about a week after his most recent buffs and suddenly he's OP. He was much more broken before 5.2 but no one knew for some reason. why complain now when he did the same thing but better back then? I'm not saying he isn't strong right now. he is.
Typical boards.
Also, I did the math
Old Veigar with 450 AP and dfg does more damage than new veigar with 750 AP.
Old veigar's combo would do ~3094 (have to factor the %hp dmg that dfg active did) so say a 1900 HP vayne since that's around her base HP at level 18
New veigar would do 3030.

( are your jungle picks. It was almost always Rengar VS Khazix) And mid lane filled with
. So he was still outrageous, just very very hard to pull off because of the Assassin meta and pressure it had on a champion like him. Now with Assassins not the only thing being viable and all the AP changes and DFG removal he is actually a champion with his own place rather than press point and click nukes with DFG and instant stun and hopefully win the game. His scaling is higher with New death cap and getting Q stacks with assists now and double stacking. So his nukes on paper on weaker but in reality not really changed at all. It is all up to Riot if he is too strong. I think he is way stronger now with people mastering him and using his Q like you are supposed to. He has a lot more flavor to him with all the changes. So you have to take into account the current items in the game and his potential with all the changes he has. I think he is a little to strong myself.