English is not my native language, and yes, I'm the original writer and... that's it, I didn't have anyone to help me, I'm also the one who rendered the text in English. Honestly, if the word Saintess is the only problem, I'm pretty happy, I was expecting much harsher criticism.
Now for the word itself. I really like materials like manga, visual novels or anime, and the word Saintess is often used there. Maybe because it is translated from Japanese, as you said, or because Saintess seemed more appropriate for the translator, I don't know.
To give some examples, with a quick search:
- Manga: the hidden saintess.
- Webnovel : the Saintess and the Villainess
- Manga again: The saintess has a showdown.
Anyway, probably because this game is inspired by those kinds of material, I thought Saintess was more appropriate. To me, it gives a "manga/anime" feeling.
I'm not saying I'm right or anything, just explaining how the word came.