The problem i think is not how fast heroine falls but consistency and believability of Characters and their actions. And yes, i think MC PoV make its easier to explain changes, because a lot of stuff and heroine's character development happens hidden from MC and player view.
But what we often see is just a 180 flip of Heroine personality, its not necessary a bad thing, but its lazy scenario wise.
I think that whole theme with Innocent, naive, pure, good-hearted, sexually passive and inexperienced heroines is overrated. We have like one heroine personality but in many different games with different appearances, but in essence they are all just the same one girl.
I want to see heroines being more active, more teasing, more dominating, more "evil" when "corrupted" but still retaining most of their Character and clear mind. Not just becoming some pregnant nympho who is ready to service hobos in public toilets, but sophisticated, strong and independent women who, with a help of Netori guy, learned new things about themselves and their sexuality. That way we can explain how (why) shy girl is becoming sexual predator, she was predator all along, she just didn't know it herself or didn't (couldn't) show it.
That's why some slutty or at least flirty and more sexually active heroines are often more likable\interesting for me. Also i think that's explain why i would like to see more milfs in NTR games, they don't have to follow this naive/pure formula.
I think i better stop now, because my thoughts are going into too many different directions at the same time.
Speaking of Miel games and separate PoV routes. How many of their games have it? I think
Shinkon Netorare Seikatsu have it.
Also i wish we could get updated mystery list at
http://www.anime-sharing.com/forum/netorare-120/updated-master-list-ntr-games-298684/ but that Second Brew guy is probably not here anymore :(