I don't like fanfiction where author are afraid to change events as it will be inconvenient for the Mc with future knowledge. I feel if MC becomes strong enough and gets all the good things then he can adapt to any thing that happens. You should read 'How much for your soul' a brilliant TDG fanfic where author is not afraid to make changes.
Ok, if MC is not going around consuming souls, why give him the ability to do so at all, seems like a wasted cheat. Why leave the shadow demon for Nie Li, it feels like MC is just an observer and he is shackled to the main story, just following Nie Li in the shadows like a stalker. At the very least I expect MC to get Ning'er and Zhizun in the harem...