I agree on all this, and I think his character is good for the role he's playing. Those who want the sharing with Neil might not mind so much that he's a slimeball, and those who think he's a slimeball are probably not going to be made to reconsider their opinion just by toning him down a bit. For me, as far as Neil goes, "what happens in the gallery stays in the gallery."
I understand that Fable has a wish to get more players involved with Neil, so that they can play through the scenes he is obviously invested in render-wise; ie those with Sarah/Neil...but if its about some sort of character that is "Neil-lite", then perhaps "Dom Alex" could develop those traits instead, and make Sarah do somehow naughtier things?
Without a substantial plot twist, eg discovery and thwarting of Neil's subterfuges, it is probably too late for any change to Neil to be believable in the context of his current "personailty", and therefore for a lot of players to actually want to change routes, which they would have to, in order to "play" with Neil. Neil, even as a "friend" or "desirable" target could currently only appeal to Route 3 or 4 players, I reckon. Any Route 2 players seem to only ever want to either avoid or cuck/subjugate Neil, and Route 1 players won't even go there.
I am going to be very amused by Fable's plot machinations in order to create this "Neil-lite", that is actually accepted by the couple willingly.......I do wonder what that might be. And even then, just how it might change the whole story.