Orally they are of similar potency, but whereas snorting OC doesn't increase the 'area under the curve' of plasma levels, hydromorphone is about x4 more potent if administered parenterally. I THINK that is why oxycodone was considered 'less abusable'.
Anyone who has snorted 10mg of each will be in no doubt of which is the stronger.
Of course, abusing HM in such a way makes it easy to OD. I always recommend people stick to the prescribed route of prescribed medicines. Altering the ROA can have unexpectedly untoward effects.
