Doctor Strange's power fluctuates. Of course, it differs greatly when he is and isn't the holder of the "Sorcerer Supreme" title - which he currently is - but it has also generally been massively nerfed since his "classic" days leading up to the 1980s. There was a time when "classic Doctor Strange" was one of the most powerful beings in all of Marvel comic books - including cosmic entities and abstract beings. He held his own against the likes of Adam Warlock when he was wielding the full Infinity Gauntlet and would regularly go up against the likes of the Living Tribunal. These days - although he has recently been made to be more respectable again - he is far less powerful. He found himself getting beaten by Hand Ninjas - the likes of whom wouldn't have been able to lay a hand on the hero when he was at his most powerful, as he had an enormously powerful forcefield by default. Essentially, he is absolutely nowhere near as powerful as he used to be.
