On the "never FMC" thing, I understand the reasoning. I also agree that many NTR games that fail seemingly do so because they are FMC, and therefore fail to invoke a sense of tension or unease in the player about what's happening to her.
However, it's a mistake to think that having the FMC's status be "unknown" is the only way to create tension and unease IMO.
I've recently been playing the Rose trial version, and holy fuck, it's one of the best damn NTR games I've every played. This is despite some things that initially put me off:
- It has a mix of male and female POV, and many sections has you playing as the FMC in a two-man party with the bull
 
- Pretty much every male characters, including MC and the bull, look like girls
 
- The standing character models are animated in an off-putting way that takes some getting used to
 
I think there is a tendency to incorrectly assume the root cause when a game fails to have effective NTR. If the game happens to be FMC, people jump to that being the primary reason.
Fact is, most devs just don't know how to write NTR well, and maybe having a male POV can better "carry" poor writing than FMC can.