IMO some of the D only players seem to be complaining about content or the that the VN has become stale and repetitive.
No kidding. Your choices are limiting character and story development and then you complain the character and story is limited.
It's analogise to going to an amusement park with only one ride and then complaining that there is only one ride.
It seems a number of D only players think DMD should have ended at Chapter 2 or end with Chapter 3. And they are correct, on the D only route, however in the D sharing route the game still has a lot of drama and events to offer.
Personally, I want to the sharing paths (and perhaps even more harder paths) are available for selection in the game. But I want this on one condition - that these choices/refusals of paths (and the decisions of the characters on these paths) will be motivated on the background of the unity of the F/D pair and dictated (or refused) thanks to the shades of personal motivations (include deviations) F or D or F / D of both as individuals (rather than just pressing a toggle button). Not like "it just has to be" anyway even if these paths completely contradict the nature of F / D personalities, or make them flat.
This allows you to preserve the integrity of the narrative, the integrity of the characters' images as they are, as individuals (regardless of the chosen path). This is what the F/D path advocates want. They want F and D to stay on their own and not turn into an inconsistent mosaic of sharp instant impulses, and flat sex dolls.
And finally, even on the clean path of F/D, this couple has so many plans and obstacles that I disagree that even on this path, the game should end in chapter 3. Rather, on the contrary, if personalities F and D were to make it flatter only in order to massively represent the whole bunch of deviations, then only such a model will very soon make you lose interest in the game (when the characters are flat and all the animations are viewed, you simply delete the game and look for something that contains interesting characters, and not only list of the modern Kama Sutra).
Also IMO of course.