Veigar is average at best.
9/10 times he's the same tier as the champ he's shooting, or lower. You'd have to get pretty goddamn lucky to have a Veigar that stays a tier above the competition for the whole match.
Not to mention sorcerers in general are fairly weak right now, so you'd be grabbing Veigar for his yordle bonus -- and yordles are mediocre to above-average at best. Especially now that everyone's running brawlers, knights. They can just weather through it and win a war of attrition.
I think Veigar is fine how he is, honestly. Sorcs could use a nudge buff. Yordles are probably fine where they are, too.
If you took Veigar's insta-kill away, you'd have to make him a 1-gold unit to compensate. There's just no other buff that would help him at that point.