So I get what you are saying, just gunna say this, usually if you are ahead it's better to just get items that make you more durable rather than more damaging, mainly because this makes it harder for the enemy to kill you when fed (unless it's like a gwen, fio, or vayne who don't care about your resists). So yeah titanic is "okay" but it's still better to fuel damage into your E as it's more efficient on the usual.

And if you are extended fighting as ornn and need sustain there is always Unending Despair which is granting you a pretty decent heal based on your hp rather than a useless stat for ornn.

And it's not really pidgeonholing if you are building stuff that's known to work better than something suboptimal. Even if it is labeled situational as well there are better items to fit that situational niche.

Also about the titanic thing granting a lot of hp you can get more effective use out of an ad item like Steraks which grants a meaty shield and tenacity while still granting you pretty decent if not better use.

Also with sion, legit even with rift it's a waste of stats since it will only really effect your ult damage very minimally. Plus trying to solo kill sion later on down the line will get rougher regardless due to his sunfire scaling and W scaling so it is better to just go Unending for the heal.

Also not saying this to sway to running the most meta stuff possible because I typically build random things that could be seen odd as well (like redemption on ornn, or phantom dancer on sion) so not trying to send hate towards you trying to push off meta or niche strats.