Veigar got nerfed (likely anyway) because he saw really good support play in korea, though he received a pretty substantial buff this patch (half a second less delay on his E, and increased missile speed on his Q), with more buffs possibly on the way.
Xerath's nerf doesn't really do much to him (he can still easily land his full EWQ combo)
Syndra was one hell of a lane bully.
TL;DR: Probably not, Karthus doesn't have that great of an early game and only really shines if he reaches his mid to lategame in relatively good shape. Viktor is actually pretty easily countered by mobility, since Gravity Field relies on you staying inside of it to do anything to you (its still an extremely powerful skill though don't get me wrong)