Well, that's certainly consistent with what you've been saying. Could you send me the raw files? jgoldstone (that first letter is a lower-case J) blah arri.com, replace the blah with an '@' and you're there.
On my side, last Friday I did two grabs on a Studio next door. Here are some ways of processing them. The ones that are slightly out of focus are the shots with the ND (room light + a very small TrueBlue meant that I was very open).
Resolve 8.2.2 (no ND in path):
Resolve 8.2.2 (ND in path, aperture opened way up):
ARC 2.3.0b20 (no ND in path):
ARC 2.3.0b20 (ND in path, aperture opened way up):
So the residual difference in Resolve 8 seems comparable to that of the ARC.
We just installed Resolve 9 next door and I will try and experiment with it tomorrow. If you can email me the .ari files corresponding to the images you are showing above, I will try them out here, compare your metadata with my metadata, etc. And I will reply to your email enclosing the .ari files that I got from my grab and you can check them out. (I'll send you the .ari attachments in two separate messages to try and stay below your mail system's attachment limit.)