That's anecdotal as we have no information to go on about those users you found from the UBI forum. The reason we put weight behind the likes of Tommy/Gerard is both are savvy users with high end PCs running 3080s. These are not novices from the internet. And their findings are validated by multiple tech media outlets, that's the thing.
Tommy can speak to the questions asked, but as I understand it he only solved the issue by disabling the HD Texture pack. Certainly for Gerard that was the case and he confirmed as much already in the Far Cry 6 thread.
When I had a 3090 I did not experience any issues with Far Cry 6, with or without ReBar and that was a month or so ago. Sure it was 10-15% slower when overclocked than my overclocked Toxic in FC6, but it didn't have any FPS drops. As I recall
@gpuerrilla is using a 3090 and completed Far Cry 6 at 4K max settings without FPS drops too. So, if there was a big issue with FPS drops not related to VRAM, we'd have seen it too, right?
Most likely those users you reference on the UBI forums have local system issues, certainly there is not enough evidence to suggest it's an issue with the game that the developers are trying to fix. I think that ship sailed when you used that excuse previously when the game launched in the FC6 thread.
As for this question - Why does it seem to be a widespread problem across a whole range of nvidia gpus and not amd? Widespread problem seems a bit of a stretch, but that can likely be answered by looking at the computerbase chart I posted earlier. Only a few Nvidia GPUs actually meet the minimum requirements of 12-16GB to run the 4K Texture pack yet we have every man and his dog trying to run it and then wondering why they have problems.
How? They have posted their pc stats of which were no slouches, iirc, various setups being intel and amd cpus.
One of them said they modified their page file, which you then put their issue purely down to that, which it could very well be.... but again, no one can confirm that except ubi developers.
Again, you say "multiple" tech media outlets as if making it out like several sites, when it is just 2 to my knowledge? Meanwhile we have TPU and HUB who haven't shown/stated the same issues with FPS dropping to single digits? No idea on other sites but can't say they have stated anything, as if they had, I'm sure we would be hearing about it..... In terms of users, I have uploaded my footage and stated that when I too enable rebar I get the same issue (with no FSR) but without rebar, no issues.... Why is it when you can clearly see my 10gb vram exceeding, fps doesn't plummet and frame latency is a smooth line? Surely if it were "vram and nothing" else, in theory, my 3080 should have completed locked up and dropped to single digit fps or at the very least, shown huge frame latency stuttering? PS. was meaning to post this a while back, but remember you were saying the graphical corruption was down to running out of vram and nothing else, well that was fixed by a nvidia driver update:
Windows 10/11 Issues
- [Windows11][Far Cry 6]: Geometric corruption occurs in the benchmark and in gameplay. [3441540]
Can't be bothered going back in threads but Tommy for 100% stated the issue was also happening at 1440p with fsr and when the hd texture pack was disabled. How do you explain that? Bearing in mind, he exceeds the specs for the requirements without the hd texture pack and that was at 1440p with fsr too.... iirc, Gerard stated the same except he also mentioned he was getting a lot of CTD, again, something I and many others have not noted....
Again, you're kind of proving my point with the whole "just because 1-2 people experience it or don't experience it" doesn't mean you can apply it across the board... until it is unanimous, you can't just take 1-2 people and 2 sites and say "vram and nothing else"...
Also, if you look at the ubi forums, you would see it is happening on a wide range of nvidia cards even with >=12GB vram.
Except it didn't as not remember all my posts with screenshots showing texture issues etc., something you were adamant was 100% down to vram and nothing else, developers announced they found the issue and were looking into, fast forward 2-3 months (?), developers released a patch, which fixed that issue for several users on here and just so happens they dropped their 16GB vram requirement down to 12gb vram requirement.....
Like I said all along in the FC thread as per the texture loading issue, maybe there is something on nvidias driver end they need to sort for those seeing fps drops or/and maybe it is a game side thing too....
The ship most definitely sailed and has circumnavigated the globe thousands of times since. HUB Steve thinks so too. 
