Wasn't it stated in the previous chapters that the Saintess an S-class guide???

na bruh she's a fraud, our MC is the tru S-class at least in this current timeline i think

In the first timeline she was, but







assuming it's the same as this time around, that's b/c she kept going back and forth between this world and her original world, which raised her guide rank each time. Unfortunately, it also caused monster gates, so yeah.