Well, I showed you that "Kievan Rus" is used in books more frequently than "Ancient Rus". How is this not "convincimg"? Is the counting rigged? You may go check other encyclopedias and come back tell us what you find out.

As to redirects, you are right. No rules prohibit creation of redirects from sensible titles. "Sensible" is pretty much inclusive and a redirect from Ancient Rus is alredy created. The types of redirects that are not allowed would not be created in good faith anyway. Under whatever name you think this may be found in English or whatever name you think the reader  looking for this article might enter into a search string, redirect is always a good idea. What's not allowed are only redirects that are POV pushing through promotion of POV term or non-existing term. Like it's not OK to make Little Russian a redirect to Ukrainian and instead the redirect should be to Little Russia, an article about the etymology and usage of the term. You cannot also invent a term and start pushing it into usage by creating a redirect article under it. Most of the rest is not a problem. Ancient Rus redirect is certainly a good idea.