I'm not a big numbers guy, but here's my thoughts as an old Veigar main.
Veigar used to hold out (not so) okay. It was rainy days for Veigar, but he could hold out, barely. At the very least, any jumps or dashes could be half-countered by Veigar's stun. Adding a delay on Veigar's stun effectively makes him useless against any champion with a dash (hint hint, almost all of them), and it becomes extremely difficult to duel anyone, limiting Veigar's high-value stuns to teamfights where everyone is pre-occupied with something else.
The very core and basic mechanic that every single Veigar main spent hours upon hours practicing, which was to land the stun ring directly onto a target or targets, is now gone. Poof. Antiquated. Useless.
You are no longer able to reliably CC ANYONE, no matter how good you are, and the stun's only use now is as a zoning ability, since you can't place it directly on an opponent (unless they are blind or not paying attention).
How good do you think that makes us feel, Riot? To know that the very thing that every Veigar main had to practice the most, (yes, it was not using E, W, dfg, Q, R successfully--it was not farming Q well--it was to land E accurately and consistently) is now replaced with an unreliable delay mechanic?
Let me just tell you. It feels fucking terrible.
And for the record I don't like the Q change either. Not because I'm a stubborn piece of shit, mind you. Making Q a two-target ability makes it so that you need to kill two targets at a time for it to be effective, especially considering you increased the overall cooldown of Q. Killing two targets with a single Q is extremely difficult in the early game. You would likely have to manipulate HP numbers by basic attacking to whittle down the HP of one target before killing it and one other with a Q, at least every now and then. However, that is a HUGE nerf to Veigar's laning phase, more than can be written on paper, because every time you basic attack to line up a double-Q, as we'll call it, you are pushing the wave, which is never a good idea for Veigar. The old Veigar thrived on freezing the lane and farming Q since he has no real escape besides stunning his attackers. But this new Veigar will inevitably push lane much more than the old Veigar, and on top of that will have a less reliable stun.
Bottom line is, these changes have made Veigar way too much risk without any reward.