I forgot to add that, personally, I get an MJ-style vibe from HydroCity Zone as well -- both Acts, in fact. But I'm gonna blab about other stages first...
It's interesting concerning the other tracks:
A >> Carnival Night, IceCap and Launch Base are glaringly obvious re-arrangements in the most basic sense: same instruments, same tempo, they could easily be merged into one longer track with no noticeable differences between Act arrangements. This is odd considering the effort that went into the rest of the soundtrack.
B >> Other Zones (Angel Island, HydroCity, S&K Zones) all carry some very distinctive differences between Act arrangements - any combination of changes in tempo/time signiture (Lava Reef/ Hidden Palace), musical style (HydroCity), etc.
C >> Meanwhile, Marble Garden and Death Egg strike me as being right in between A and B: There's a slight tempo change and swap from a major chord to a minor chord between acts (MGZ), and some rather slight differences in instruments between Acts (more noticeable in MGZ; I hardly hear anything in DEZ), resulting in what I've perceived as "overall just the same song" (A) in both acts as opposed to most other songs' "noticeably different, separate arrangements of the same tune." (B)
Now, as for HydroCity...
I said that both acts give me different stylistic vibes, from the same '80s-to-'90s era MJ tracks. By this, admittedly I mostly mean that with each Act arrangement, I can imagine hearing Jackson's vocals fairly easily over either version. This is just personal speculation, with no real "theory" to speak of, that I will gladly chalk up to [Setsumaru? Okay, Whoever] just doing a great arrangement. I don't really feel strongly one way or the other, save for the fact that, with the limited information we have, current signs point to being [whoever]'s arrangement.
...As I've asked before, am I making sense? I imagine I spend longer typing responses than most here in an effort to come across as clear as I can, but I wind up taking so long that I often lose focus of my original point, so I apologize if I fail at clarity.