I believe AI (or AGI) that is better than humans is quite far from done. May be the technology available today can generate better-than-human AI (without going the quantum way), but we probably lack the models or structures or simply the scale that can make this happen. Or may be we are missing some fundamental discoveries about cognition and intelligence.
But even if we develop powerful AI, why are we so scared about it? Why do we think that a powerful AI will be stupid enough to stay interested in Earthly matters or humans when it has an entire universe to go to?
EDIT: From time to time I hear someone established and reputed cautioning against a powerful AI. I am just curious what I do not understand
Example (an year old post): https://www.washingtonpost.com/news/the-switch/wp/2015/01/28/bill-gates-on-dangers-of-artificial-intelligence-dont-understand-why-some-people-are-not-concerned/