If Veigar must be changed, Give him a new W
Because as it stands he will no longer be able to complete his burst rotation with E being the way it is. You basically turned him into a less mobile more squishy Nidalee.
except with his R nerf his ult now has a pretty large chunk of damage missing. 20% less damage...That's a large number in terms of league of legends balance.
What I mean by nidalee is he becomes like her in the sense of throwing spears until you hit then proceed to use your spell rotation.