The Criticism is not of the character but of the Player's freedom of choices in the Playthrough. As for "not in any way bound to the MC" She would still be an old hag about to get her ass kicked further away from town if it wasn't for the MC. Please don't be that guy who starts the whole "cuckolding is awesome" argument again. Everyone has their own kinks if everyone was similar we would live in a very boring world. If someone wants to play the game as a "conqueror of everything in sight" kind of character then there's nothing wrong with that same as there is nothing wrong with anyone who enjoys a game with a Heavy NTR storyline. To each his own as the saying goes.
Tinkerer could easily split the storyline with making all he NTR optional he has faced backlash from his patrons over the force cuckolding before IDK why he doesn't just keep it optional.
Her story is far from completed and you might be shoked how popular a theme with a bitchy character is, that by a specific event or a row of such changes her way completly.
Considering that the Priestesses of Quietesh were never meant to know the blessing of motherhood our own little divine intervention might create such events in the future.
At the moment she is sleeping around freely, but soon she will have to commit herself to something...
Why no one asks where are the other acolytes of quetsh ? They were sent to the strongholds but shouldn't they return by now?
Dureing the war with Nergal he cursed those who survived and most either are still cursed or died in the aftermath... not to mention that some/most never made it to savety... read the story of the sister that developed the enhanced fertility potion for example.