would you recommend cutting it entirely?
Probably, yeah. Replacing it with the different suggestion would work better, though you could just clear up the description and go without one there.
As for your second point, the final note was intended as a sort of "reveal" at the end of this article's story.
You CAN do that. But you really, really need it to feel earned. Think about a murder mystery — a satisfying reveal can only happen if there were sufficient clues along the way. If, at the last chapter, it's revealed that a character we've never heard off before committed the murder for reasons no one will have suspected, readers will feel totally let down and cheated.
Same thing here — if you want to have the big reveal, you need to have some pieces connected to it earlier. You don't need to spell it out beforehand (in fact, I would recommend you don't) but the reader has to see where it came out of.
In fact, if you do it right, you don't need the note — you just need the final incident. If you were to hint that there's something foreboding and non-human about the place, then have the incident with the imposer (and make that a little clearer as to the intentions of the thing), the reader ought to be able to reach a similar conclusion themselves without the convenient note at the end.
As it stands, I would absolutely not be able to tell what's happening without the note — so it actually even seems a little weird the SCPF reached that conclusion.
phrases like "pocket dimension" and "temporal trajectory" were a bit too sci-fi and out of place
I've seen both used in SCP files. I don't see any reason to replace them.
did you feel that the core concept was strong, and that it could be suitable for an official SCP?
I feel like one of the most prevailing myths on the site is that stories live and die by core concepts. Nearly every single core concept can fly, as long as the story you're trying to tell around it is interesting. That's why I focused on how you're telling your story.
edit to clarify that last concept thing:
Feedback given here often talks about how the core concept isn't interesting. If you look into most of it, it's due a lack of an original story. You've got a pocket dimension (which is a common trope on the site) but you're trying to tell a story around it that does seem fundamentally interesting, outside of the clumsy execution.
