Ok, I just finished trying out two other games. Final Fantasy 16, which according to SpecialK utilizes GPU decompression with DirectStorage, and it does NOT have any issue at all when spinning the camera dropping frames, nor does it stutter when rapidly flinging the mouse wildly... and Ghost of Tsushima.. which also interestingly does not have any issue whatsoever dropping frames nor stuttering when rapidly flinging the mouse around... considering it's ported by Nixxes.
I'm beginning to think this is an implementation/engine issue more than an inherent API or IHV issue... and I think we have some good data points thus far.
We have:
A Nixxes game with Insomniac engine (Ratchet and Clank, Spider-Man 2) - which exhibit massive frame drops and hitching when spinning the camera or flinging rapidly with the mouse on Nvidia
A Nixxes game with Sucker Punch engine (Ghost of Tsushima) - which does not exhibit any issues when spinning the camera or flinging rapidly with the mouse on Nvidia
A SquareEnix game (Final Fantasy 16) - which does not exhibit any issues when spinning the camera or flinging rapidly with the mouse on Nvidia
A Capcom game (Monster Hunter Wilds) - which does exhibit issues on both vendors, which can be fixed with mod to decompress before on both
To me, this data suggests:
Nvidia doesn't have an inherent issue with DirectStorage that AMD doesn't.. but rather Nixxes implementation within Insomniac's engine is causing an issue specifically on Nvidia hardware.. which doesn't happen with Sucker Punches' engine... and that the issue can happen to both IHVs, as evidenced by Monster Hunter Wilds by Capcom.