It might be your preference, but I disagree.
It a part of Veigar's identity; he is not just a mage, he is a ridiculously powerful mage (infinite AP scaling) who lives for little else than total destruction. He turns other mages strengths against themselves ("You deny the darkness in your soul! You deny your power!").
Thematic identity aside, from a gameplay standpoint, it puts him in a unique position. He is one of League's Counter-Mages. Kass also fits this due to his innate Magic damage reduction, but Veigar does it in his own way; nuking mages to Kingdom Come.
If you just crank up his AP ratio, then it homogenizes him; he just falls in line with the other burst AP mages, because part of his unique gameplay pattern is lost.
Instead, I think they need to encourage Veigar to use his Cage in ways other than just trying to land the stun. His E has always been, for all intents and purposes, just a circle-shaped skillshot. You didn't try to get them in the middle, you tried to stun them. And yes, the delay makes that more difficult. However, I had a thought: what if his spells interacted with his E? I go into more detail Here but basically, let his Q and W have different effects if they pass through E's zone, such as widening W's impact area, or maybe making Q split into multiple projectiles.
This way, if you miss the stun but get them in the cage there is actually some gameplay. This could actually give Veigar a reason to try to land people in the center of his cage - if they run, all the more likely they'll hit the wall and be stunned, but if they don't, Veigar is empowered if they are trapped.
This only furthers Veigar's theme and feel of "ridiculously evil and overpowering mage" - you're trapped and he's raining spells down upon you. It even fits his lore, considering he was locked away in a prison and went insane.
But, that's just what I'd personally prefer.
