Oversight (as in design, not QA) - is not a "bug". It's oversight, hence the specific word.
Oversight is - tweaking a class in such a way that some of its abilities become OP (unintended) in some situations that were not considered at the moment of tweaking - i.e. overlooked. Now if design oversight is a bug - then playing that class would be exploiting. And all players of that class should be banned.