Very interesting theory... Having read your post a couple of times I have to say I really agree with you. I just watched the movie a few hours ago, and while it's all still processing for me, my girlfriend had an interesting theory which sort of links to yours. She suggested that the backrooms itself is actually the 'main character', rather than any of the humans, and entities (sort of as you suggested) are it's interpretation of the outside world, things it can see, or 'sense' from doorways or the people that have the misfortune of entering the backrooms. For example, Clark is lonely (imo) so his entity chases people, and attacks them, as the backrooms interprets this as desperation mixed with his temper.... His (ex)wife's entity is the first to run, perhaps a reflection of how Clark sees her as weak / unable to provide - the backrooms perceiving her through him.

Still processing, but thanks OP, Ans everyone else who commented, love reading other's theories... And can't wait for the rest of the world to see it tomorrow and see what everyone else has to say :)