He just got some fixes on 9/1, I'd rather see what happens after a bit more time. To me he feels fine.
He can have strong impact when used properly, but that comes with his abilities feeling weak or unreliable when solo. His W's power is focused on Unstoppable and Brittle. The %current HP allows him to farm while reducing his overall kill pressure (which I love, honestly. Everyone complains about tank damage and reliability, and Ornn is not that). He's durable and strong in CC and has a strong debuff, at the cost of his reliability and damage.
Besides, at current 42% WR (and gradually climbing after his recent minipatch) with a 6% pick rate, I'd say he's moving along pretty well for a still super new team reliant champ (like tanks should be). We should just see where he plateau's before jumping for more buffs and changes, especially right before Worlds.