I don't want to be a contrarian, but as tough as Dormammu is, he'd be quickly beaten into paste by Yuga Khan. This guy was laying waste to the armies of both Apokolips and New Genesis nearly simultaneously, not to mention wielding the full power of the Source as almost an afterthought.
Dormammu is powerful. You'll get no argument from me on that one. But against Yuga Khan, he is hopelessly outmatched.