veigar has < 30% win rate in master+ since patch 5.4, 0% in the last month (picked 4x and won 0).
its because people recognize his weaknesses at that level (to dive champions and poke(no regen/spell vamp and low health pool)... and assassins) and people who are capable of forcing him out of lane entirely to miss cs, it severely gimps him when he doesn't have his farm.
its so easy to deny a veigar or just towerdive and pop him from 100-0.
because his stun isn't instant, he can not do anything other than flash, tower intimidation, team peels, or die. there is no wiggle room, he has no outplay mechanic. he is team reliant now more than ever.
this should clear things up - dabox quit.
bjergsen who occasionaly played veigar in ranked hasn't played him at all since 5.4, has stated who the meta champs were (zed and viktor being the strongest) and urgot was a niche pick to counter those dive assassins, and several others were sub par but could accomplish things. veigar didn't make the list (among 15mid laners he mentioned).
other players like scarra, hotshotgg, pobelter, faker, XWX, all have stopped playing him entirely.