For the MC to have great development as a character, a universal event (that occurs in any route and alignment) must occur. The only event capable of significantly affecting the MC would be Neil's death. I don't know about you, but I don't think DPC is going to kill Neil just for the MC to develop as a character.Honestly i wouldn't put it past DPC to make dark turns at the most unexpected situations.
Also, i won't agree with you regarding MC development even if it's plausible and logical. I much more prefer to look into possibles ways MC can develop and branch into than regarding what has already been developed. Like DIK MC reckless and violent nature getting more and more driven into overdrive for the smallest stuff, this can lead to sudden turns.
But i like dark stuff... at least dark stuff that i can see coming.