The way Kylo Ren might see it is that the Earth must be strong with the Force to have so many superheroes on it with "Force powers" that he's never heard of. I am sure Kylo Ren would like to d o some of the things Doctor Strange can do. The ability to turn into a big Green monster might be useful too. The Earth would otherwise be a dull and boring backwater planet without those superheroes and villains on its surface.