There is a crucial difference though, the search engine links back to the content. If Google would just display the content on their verbatim, it would definetly not be considered fair use. Even like this several countries have restricted what Google can do when displaying e.g. News.
Somehow building a list of pointers to original content does simply not have the same ring to me as a product that rehashes all of the content. A rehashing of content sounds to me much more like, for example, publishing a sequel to my favourite book. After all, a sequel is just a rehashing of the same characters in new adventures. If we can't do that, why should Copilot be fine?
My point was however that I'm just utterly failing to see how the youtube-dl test thing could be more of a copyright problem than this entire thing based on millions of others' works that is Copilot.