I actually disagree that DDL is a dating sim or even a "deconstruction" of the dating sim genre at all; I'd call it a psychological horror game that uses tropes of the dating sim VN to disguise and inform its horror. If DDLC has a message, it's about empathy and games (or even media) more broadly, and the dating sim trappings just serve as a part of the delivery. It's when the game breaks the fourth wall, so to speak, that you get to its intent, and by that point we see that the dating sim genre is almost tertiary to the central idea. The reason it seems like a vapid or shallow entry to dating sims or a weak commentary on them is that it isn't trying to be either of those things.
What it does most effectively is, as a psychological horror game, set the player up with the most saccharine onboarding you can get - a fluffy pink high school dating sim with all the cliché tropes solidly in place - and then chip away at those, slowly at first and then drastically. It's a cheap but effective tack, because dating sims are a style of game literally made for the express purpose get the player to immerse themself in the story and characters so much that they form strong emotional bonds, "falling in love" (with or without quotation marks) with the characters and world. Beginning with the trappings of a dating sim is an easy way to draw your empathy and affection into the world quickly and directly, to get you immersed and therefore more susceptible to the horror, character-related or otherwise. Many of those moments do revolve on "oops, it's violence!" shock factor or "All this happy-seeming stuff is sad, actually!" kinds of "drama." It's definitely not particularly deep or mature in that regard. I will say, that very first big reveal - walking in on your childhood friend having hanged herself - is really effective from a visceral shock standpoint because of the whiplash, even if you absolutely know it's coming (I first played it a few years ago, but while I didn't know exact details I knew full well that it was a Fucked Up Game and not an actual normal dating sim).
But even more than that, oddly enough, the moments that really stuck with me and Actually Scared me were the glitches as things started falling apart. Getting kicked back to the title screen as though nothing happened, welcome back, let's play a sweet dating game! was effective as a discomforting, uncanny moment. I know that this isn't a new concept in games, but the a/v design and timing of things starting to glitch out, to break down as a game, even the "jump scare" glitches out of nowhere, really made an impact on me. I think the format of the VN/dating game also helps inform a few of its segments like the tall girl's suicide. The horror of that scene, to me, lay not in the brutality or shock of the violence, but the lack of control/runaway train feeling. Iirc you can start trying to steer things away, try desperately to defuse the situation or escape, but between tech/reality glitches you keep getting dragged back in as you see the inevitable continue to approach, and by the time she actually stabs herself it's not so much horror at the violence as sadness that you saw coming. Then getting stuck in there with the body for days was also, while gruesome, effective insofar as you were literally stuck with the grim results staring you in the face.
The last act with the reveal and denouement of the in-game character gaining sentience and being mad about it was interesting enough, the "infinity room" was memorable, the game files mechanic was neat, etc. But at that point I think it's pretty clear the game is more about empathy, desensitization and emotional connection in literature and games in general, with dating sims as a jumping-off point and a pointed example, because as as exercises in empathy, they are particularly strongly suited to the message the game is making, as a genre.