Lunarians are pretty BS considering (I think it was) Watatsuki no Yorihime beat Reimu, Marisa and others at their own game single-handedly in Sinner in Silent Blue when they went to the moon. The newest one is pretty much about the final boss Junko holding a grudge against Chang'e's husband and by extension her and the Lunarians for her son's death. Events of the story follow and whatnot.
Overall, I believe it was implied somewhere that Shiki Eiki is probably the strongest character in the series. It was in one of the written material. Yukari mentioned that Eiki would defeat her, Reimu and Yuyuko if they attacked at the same time. I mean, techincally Mokou and Kaguya (possibly Eirin as well) are Op because Immortal, but you know.
Overall powerlevels are relative otherwise as Spell Card bull makes it all about skill anyhow.