Vel'Koz has been overtuned for more patches than I can count now
He was weak and got overbuffed. Few people seem aware of it even though he's had the highest mid winrate for many patches now. His level 6 burst is LB level from range. He scales well and even destroys tanks. His waveclear is good. His CC is good.
His only weakness is mobility and it's not even that big of a deal because of how easy it is to play from far back if you need to and are worried about the jungler. He's not hard to play and way too rewarding. I've seen a Ziggs get legit 1 shot under turret from 90% HP purely by his level 11 ult. and the Vel'Koz was only a kill and 20 cs ahead.