Oro is seriously bad news.I'm... not actually convinced it is? Naively, sure... but Leaf + Hazou means that we cede the rift to Leaf which means them using it for war. I'm not actually sure whether it's better that Leaf be using it for war than Oro be using it for Oro-level experimentation.
He's a researcher who just gets stronger over time. He was one of the strongest ninja in the world before we handed him dragon-biosealing augmentations and Runesmithing.
When we asked him if it was possible for him to coexist with the existence of other agents long-term, he laughed and called us an idiot.
He is necessarily one of the final bosses of MfD.
If we hand him the rift, he might decide to fish out Essies and mind control them with biosealing, basically inventing Edo Tensi.
If Leaf has the rift, it will fight a bloody war, then spread uplift, and eventually become the kind of power that can permakill or restrain Orochimaru.
Not *ideal*, but much better than helping Orochimaru ascend to ultimate power.