Veigar Q is the problem behind Veigar
We have all seen the raging go on about Veigar in the last months since he jumped back up into popularity. The focal point usually seems to end up being his ult that does a ton of dmg to whomever it hits. Veigar has always had this potential, and defines him as who he is as an anti-mage mage. He is also not as bad with his rage cage like he used to be when it was instant cast and your opponent had no chance to escape it or not touch the wall.
What has really changed Veigar towards the overturned side is his Q. I will first refer back to when it was changed to a skillshot as the first problem. I understand Riot has a fascination with removing point and click abilities and making them a skillshot. In the case of Veigar, I believe this helped him a lot, maybe too much. His Q now has a longer range of 900 instead of the 650 his point and click version had. This provides him a potentially safer laning phase as an expert can use timing of minions moving to safely last hit at an extended range. This allows him to stay closer to tower in a safer spot as well as having an easier time avoiding damage from his lane opponent.
2nd, Q went from hitting one target to two targets. This was probably the biggest boost to Veigar. Great Veigars are differentiated from the bad Veigars with their ability to claim two minions with one Q, getting good return on the skill. Veigar in this form saves a ton of mana and has less CDR issues than he used to when the skill had to be spammed more for farming waves.
3rd, the recently added AP for assists is just crazy. Veigar is able to easily finish games with two free items worth of AP now from all the AP thrown his way now
Back in the patch 5.4 where Veigar had these changes made, Riot made a statement of tackling his reliability in making rage cage no longer instant in order to allow his Q changes to happen. While this is true and makes him harder to catch an opponent in one vs one, it needs to be evaluated to whether or not he gained way much more in his Q power than what was lost every else. Cause why bother with a rage cage if you have gained enough bonus AP to blow someone up without needing it?
Just my feeling on the current state of Veigar.