Literally though, give the temporary-saintess responsibility to a 15 year old girl, then have her child end up being the true-saintess. Even if there wasnt a shady deal involved, that just means the child will always have been the cause of the temp-saint's downfall.
Or perhaps it was the reverse-there's a true saintess eventually, but before her, lets give the powers to her future mama and not tell her about the child/make sure she's actually a good person ╮( ̄▽ ̄)╭
The shady guy literally said the goddess was irresponsible for giving the role to a 15 year old girl and then taking it away, before making the deal to extend her abilities. She most definitely was a temporary-saintess at one point, until leticia was born.
*spoilers*
Also, as someone who's read the spoilers from other comments Im certain in the fact that she was at first a legit temp.
I’m thinking everything would’ve worked out fine had that dark magician not interfered. I’m pretty sure it was mentioned that temporaries had often been used in the past with no problems. The difference this time is some evil person manipulated a young girl to get control of the Saintess powers. Josephine probably became evil because that guy infected her.
Ok but why would they make the daughter of the fake saintess the true saintess? That's just a set up for disaster, worst idea imaginable.