Power is not really as frightening as it seems to be. I mean, sure, dragons are amongst the most fearsome creatures in mythology and fiction but their sheer power is not the thing people find most frightening, deep inside.
What powers do they have? Usually, especially Greek dragons in mythology, have a wide range of powers. Usually poison in some sort or other. Eyes, even hundreds of eyes. The ability to never sleep. The ability to see the future. Sheer size that puts them on a level with a national catastrophe rather than just a monster with fangs.
On a side note, Greek dragons usually don't breathe fire ...
Artificial Intelligences are also considered some of the most fearsome things, fortunately enough, only in fiction so far. But just like dragons, their most frightening feature is not their sheer power.
What power do Artificial Intelligences usually possess? Taking cue from real projects such as The Blue Brain, they usually have vast computing power, which may be put in various uses, from cracking and hacking to calculating intricate plots and inventing horrendous things.
For an example, the time travel device used in the Terminator series films was invented by the Skynet Artificial Intelligence and not by humans.
So, dragons and artificial intelligences, though usually residing in very different types of stories, one in science fiction and the other in fantasy books, have awesome powers but this is not what makes them so fearsome to us mere mortals.
What makes them so fearsome is their way of thinking.The cold thinking. The Virus Thinking.
What does that mean? It means thinking beings, be they dragons or artificial intelligences, that can think and reason and plan but have no compassion, nor feelings nor any kind of understanding or empathy with humans, with us.
And that's frightening. A fearsome predator that sees us only as food source. A cold artificial intelligence that sees us only as tools to maintain its devices and computers. In all those cases, these things will wipe us out on an individual or planet wide scale without giving this another thought.
Think of some of the worst dictators the world has ever seen. I think these cold thinkers, these dragons of myth and artificial intelligence in science fiction stories will be worse.
But wait, we are trying to build artificial intelligences in real life. Maybe we will get the chance to see cold thinking in real life. I don't think this would be much fun ...