His base health is a joke. With the average game length having been dramatically reduced, his passive health gain can no longer bridge the gap (if it ever did). That by itself wouldn't be a big deal if he weren't also mediocre defensively in other areas. His base armor is nothing to write home about, and his shield is expensive and awkward to use since the time recast nerf all but guarantees it will be broken before the damage portion.
His late game damage is also pathetic. This is patently unfair, as he does practically all of his damage short range and is one of the few champs in the game capable of missing 100% of his kit's damage. This actually becomes a huge problem if you do well early and gold-sink your team, because your success won't last if you don't leverage it into an early win. This problem is only exacerbated by the disparity between defensive items and offensive items.
His passive health gain does have interesting implications for certain items though: Cinderhulk, Sterak's, Warmog's, and Titanic Hydra all scale infinitely with health, and of course Spirit Visage will scale infinitely with Warmog's. Too bad you don't hit late game anymore.
His passive is basically nonexistant as an offensive measure, short of rushing structures. One slow, and you're done without touching anyone. The wind up is ridiculous too-- so it's not like anyone's actually going to be close enough for you to hit regardless.
Winrates for CC heavy tanks are misleading. It's not a reflection of their individual strength, but their ability to support and round out a team almost regardless of comp. Not exactly a great indicator for balance in a vacuum.