Just because it builds a very elaborate fantasy doesn't change the nature of the fantasy. I think it's just terribly bloated because it became so popular, and/or mrdots has a problem with brevity. You even pointed out how D is like a naive fucktoy, totally unrealistic, and that's an entirely valid observation. That's not a new thing, she always was that way (except in .01 she was more sassy and adult, but that was quickly revised by .03 or .04). Along with how mc behaves like a horny teenager, it's probably the most common criticism you'll see in this thread. I'm just saying that D behaving like a naive loli fuckdoll and having no agency is a feature not a bug.
Whereas Melody is a much more focused and concise narrative, I think he is just sort of winging it with DMD, as it's his first story and he never expected it to take off the way it did. He's trying to provide his most diehard supporters with more of what they really want in order to fund the creation of his newer works.
This seems a rather inconsistent analysis of MrDots' otherwise consistent storytelling style.
While they are certainly adding in more ideas and responding to the fans as they go along (e.g., Season 4 plans), they had also telegraphed the grand strokes some time ago. Wasting episodes with bloat for no reason other than fan service is the opposite of their creative style: as Jeff has clearly mentioned, elements in their stories exist to build upon and not as mere filler because they ran out of ideas. The story is always being served, essentially.
DMD had already taken off before Melody was brought up practically overnight and in response to Patreon's ban of the former game - it wasn't the other way around. Again, we know the general endgame for DMD: it's just that the path to get there has been altered due to timing from funding and development delays (due to parallelism), circumstance (the Patreon ban and parallelism) and some rethink from community interaction (e.g., bestiality) plus the opportunity that Melody provided to continue elaborating on details of the DMD story. Acting as if DMD has been generated in a half-assed manner seems a grossly off-beat base of any argument you could possibly offer here.
Instead, it's more a simple matter: MrDots' team decided that their definition of NTR can't exist in a highly specialized manner of viewing the universe, which allows for the MC to cheat and D to only act under his controls. So, D's additional freedom to swing/swap on her own - even with prior MC general consent - can never occur, because they act as if that falls under NTR (again, even if prior consent was offered). This also blocks her ability to be enabled for cheating to the same level as the MC. Sure, you are playing as the MC, but we have also been provided D as someone equally as important to this story overall - treating her like a Stepford Wife (in symbolic form) is certainly an interesting option to offer in the game, but it's either that or vanilla (i.e., fully dedicated path). So, the prior history between them seems rather misleading if you are on a non-dedicated path.
Analyzing that point in DMD's context ... for a significant portion of the story, our MC's stated goal - despite his lusting - was to free D from her mother's virtual prison. They then grew to talk about everything from living together (now in progress) to marriage (now openly proposed) to a family (still open), among other things. As D's freedom to express herself has grown, she has naturally let her sexual side fly in ways that her repression likely helped to launch after the openness she found with the MC. And now, after all this development ... the MC calls the shots for her life, under the guise of a loving fiance. Because he still wields the power multiplier of being her father. A beneficent cad.
Of course some people will look at this and naturally call foul, given the history we've seen thus far. This manipulation by the MC applies mostly to the non-dedicated D paths, of course: everything from a single liaison to a full harem. For, in the dedicated path, we can at least limit the MC to the same experience range as D (to an extent); however, in no path can D continue to grow into her potential that has been clearly offered.
I actually play both the dedicated and full-out paths for each installment, which makes the differences in their abilities to choose even more stark in the playing experience. Truly, given that MC is a manipulative son-of-a-bitch for the non-dedicated paths, they should have considered altering his dialogue far more than simply showing concern for juggling competing affair schedules: this character should be portrayed as the selfish ogre that he is, helping to rescue his daughter from one controlled situation and grooming her for another. I feel this is a failing in the portrayal of the MC in DMD, frankly: we as players can see what is happening, but the MC's disposition in both types of paths is otherwise quite similar, as if he's oblivious to his controlling manner (or is simply a psychopath) - this creates much dissonance in the story with D as the other protagonist, I feel.
Therefore, a practical option would be to grant the other protagonist - that they took endless episodes to build up - with the ability to shake up the story and meet his level of craft and/or duplicity: give her a life beyond a happy cuckoo (which would make the non-dedicated paths FAR more interesting.) It's not as if MrDots hasn't done this in parallel work with Melody and shown it can be effective, even if you are ostensibly playing as the MC in that game. Indeed, I often hear a consistent refrain of how the story now feels on cruise control: while I don't feel that's true, I would wager part of that is because the lack of friction in the main storyline (even for non-dedicated path) outside of the modelling competition is rather low. There's only so far you can go with entertainment value when a MC is successfully juggling schedules for their sexual affairs and cheating on their fiance (constantly) as the primary style of personal relationships to explore.