it may be that the devs have a tendency towards lovey dovey stuff in their real life mindsets. that could have influence on the stories and scenes, because one would naturally put a bit more attention to what one really likes, and the outcome coud be like this; love routes appearing as more.. 'polished' as you call it. makes sense.
for the epilogue, seems to me that Marty does it all on his own; there's no telling if- or how much, cBob is still partaking.
so per say the game is finished, with Marty doing touch-ups and when he sees fit doing the slave part of the epilogue, and no way of finding out if cBob is in it. i assume not, because there's still this his style, this teensy bit esprit that was in cBob's writing, hard to grasp but i kind of feel that on gut level.. and it's increasingly missing in book4 and not there in the epilogue. Marty did vastly improve his writing, true, but there's a difference. i can't even really describe what it is.