I agree with this. Tanks in general should not be able to deal significant amounts of damage unless they're a hybrid of a damage class, yet currently many tanks deal way too much damage, and Ornn is the most egregious example of this. He was originally designed to be a champion who traded off damage and laning power in general for immense amounts of CC and team-wide late-game scaling via his items, but now he's become yet another hyperscaling lane bully, as we've seen with several other champions that get overbuffed after their release or rework.
I think part of the problem with Ornn right now is that his Masterwork items just don't really have much presence: they're not statistically efficient upgrades, nor are they meant to be, so they only really come online towards the very late game, which rarely happens at the game's current pace. In addition, they're just stat boosts, and thereby provide no interesting gameplay of their own. Because of this, I feel his items need to be reworked, so that he offers purchaseable bonuses with meaningful gameplay effects, potentially which interact with Ornn specifically, and which can have some use even early on, even if they shouldn't be mandatory. Adding late-game scaling via a mechanic shouldn't mean that that mechanic shouldn't exist until the late game, and in this case it could still work by increasing the gold cap to every champion's build.
With Ornn specifically, though, his current excessive damage comes from his W, though even after that, Brittle is a pretty strong effect. I think above all he needs a damage nerf, but beyond that it might help to make some of his damage flat damage, rather than percent health damage, as right now it makes him far too good against other top laners. Ornn I feel should be able to jungle, and changing his W to flat damage could potentially give him the basic clear he needs, both for waves and jungle camps, while still letting his on-hit effect deal more damage to tankier opponents.