I'd say his AP ratios are too strong (1.3 on ult is dumb), but his real problem lies in his lockdown. He has 3 slows making it so that a good E cannot be avoided (2.25 stun is also dumb on a non ult) unless you're mobile or burn flash, he has a massive shield, and if he gets into trouble, he has a gtfo button that is capable of a full heal. Frequently if you want to go in to kill him, you have to do it twice because he full heals.
He's got too much, something/somethings have to go. I'd say keep most of the AP ratios (tone down the aforementioned 1.3 ult ratio,
has a lower ult ratio), reduce the ult heal, and make his CC less intense, probably by making his passive slow less, deal less damage, and give him a speed buff for less than 5 minutes, and giving the Q a slightly lower slow. I'm not saying gut him, he is fun, he's just too much of everything.