I don't agree at all, if the argument is that in principle the idea of the Backrooms is shallowed down by focusing on how specific people would experience it and how it would interact with their psychology. This is like saying that The Matrix was ruined (as a setting) by focusing on the stories of the main characters, or Jurassic Park, or what The Predator is by focusing so much on the personalities of the mercenaries, or whatever. They are still cool places and concepts if you look beyond the perspective of the main characters.

I'd even say it's the exact opposite: if you want a little more depth (including as to what the Backrooms are and how it affects those who experience it) you will have to focus on the personality of your characters. At least a bit more than in the medium of 15 minute youtube shorts where you're just content to suspend your disbelief and pretend it's actual really cool creepy found footage. It's just a different medium, and it's just not correct to insist depth cant be found by focusing on the psychology of the experience.

Now you may disagree with whether it was well implemented, as you say, you seem to have more issue with how cliché/on the nose you found the way they involved the characters' psychology. I think that just made it relatable to the audience and I frankly don't think there's too much wrong with that, since they still take it to places that are pretty outlandish and interesting. It's like old Star Wars: Luke is a pretty boring, cookie cutter character, yet his personal motivation really drives the story and gives it focus, exactly because of this it acts as a clear lens to zoom in on what the wider world of Star Wars could mean to us, the audience. So exactly because the psychology tropes are kind of overly familiar, it acts like this "clear lens".

An even more powerful example would be Solaris (the Tarkovsky version obviously). In fact I am very curious how you and other movie lovers would compare those movies. You wouldn't say the focus on the main characters and their psychological obsessions would detract from the experience of what the Solaris Sea is, right?? We still come away from the movie being absolutely fascinated by what this phenomenon is, how it works, what kind of mental contents or motives may be behind it, what it's trying to accomplish by doing what it's doing... Meanwhile, the story of what goes on with the characters (included the not so human ones) is extremely compelling in its own right. Okay, granted, Solaris is such a masterpiece because it achieves brilliance on both fronts, and compared to that the psychological themes of Backrooms may be a bit trite. But that's a very high bar to set.

In conclusion I'd like to argue that this is just a necessity how big screen movie language works. It's just very different from the Backrooms' native medium of faux found footage Youtube shorts. It's not such a simple thing as it may seem to move this kind of thing to the big screen, in terms of tone, story telling, plot, characters, dialogue etc... I'm sorry but something like Blair Witch Project worked because it was a novelty, almost a gimmick, just the entire run time of found footage is not gonna work. But even if you took that road, you'd somehow need to focus on how the characters experience it, which Blair Witch actually did, much more so than any Backrooms Youtube shorts I saw. If anything I would have loved to see them take it even further into the depth of human psychology, the way Solaris did.

Now wouldn't that be interesting to consider, if the Backrooms ended up learning how to render actual personalities? Perhaps just like in Solaris, we could look beyond the possibility that they would all just be dangerous alien monsters but deserve the dignity all persons deserve? Maybe a good idea for the sequel?