The champs you picked OP aren't bad, you just ran into bad players. The fact that you nominated Warwick just highlights this.
The current meta right now is TankyDPS/Attack Damage Casters are king. Who do they counter? Usually the squishier, but very powerful carries.
Veigar is in an unfortunate position because in order to be strong he needs to farm minions with his Q. Unlike Nasus who has a similar mechanic, he's as soft as a feather pillow. Also, unlike say Xereth, who also does not have an escape and is soft he has a much smaller range.
On the AD side we have a similar issue. What AD carry has no flash, dash, or passive movement speed? The answer is Ashe, Kog'maw and Twitch. Looking at those three however, Ashe is understandably the weakest due to Kog's range and Percent based damage and Twitch has his Stealth.
Finally, there is Mundo. Mundo...is in this weird place right now. In an era where Most if not all Bruisers have a form of gap-closer Mundo has his Cleaver and his Ultimate, which is nerfed due to the crystal aura. He cannot build straight damage or he'll just die, but he cannot build straight tank because He'll be ignored until everyone else is dead. And so far trying to hybridize with him hasn't really proven effect.
TLR, Veigar Ashe and Mundo due to power creep and unfriendly mechanics in Dom.
Surge suits him fine.
Also Cleanse or just some Tenacity (I prefer Cloak+Dagger)