Wanna know the problem with Veigar?
His E cooldown. Back then pre-rework it was a higher cooldown, effectively making a huge window of opportunity once it's down. Right now, the fact that it's been shortened by the rework (which was invisible because he was garbage otherwise - until he got buffed several times on his reliability, which is good ) makes him very strong, especially lategame with 40% cdr, it's up quite often. I personally would not have nerfed the damage of Q/W, but increased E cooldown by 2 or 3 seconds. Anyway, what's done is done, I'm not sure if Veigar is still top tier.
Tbh, I'm not sure the old instant version with ridiculously high CD was less healthy than the current one. At least when his stun was down he was done for. Now he just runs a bit and has it again.