I went through all of my Modern Warfare and Cold War mouse settings and class setups, and in both games I'm using 2560x1440p @ 165Hz, and the in-game options below. On Modern Warfare, I mostly use Iron Sights, one setup with Monocle Reflex Sight, one setup with G.I. Mini Reflex, and my 2 Warzone setups have the VLK 3.0x Optic. On Cold War, most setups are using Iron Sights, a couple setups with Millstop Reflex, and currently have the Kobra Red Dot on my M16.
It's certainly difficult to express the exact problem I'm having but in Cold War my aim is very inconsistent specifically when it comes to ADS tracking. On the other hand, I have no issue in Modern Warfare across any of my Loadouts regardless of what gun I'm using. I'm able to hipfire accurately and lock onto my targets quickly and accurately when I ADS. To me it feels like there is some mouse acceleration or deceleration going on. I did add a config option today on Cold War ("mouse_horizontal_look = 1") that some people had success with, and I was going to do some testing with 1.78 on Cold War to see if that matches up closer to what Modern Warfare feels like.
Mouse Sensitivity - 6.0 with all multipliers left at 1
ADS Mouse Sensitivity - Relative with both multipliers at 1, Transition Timing of Instant, and Monitor Distance Coefficient at 1.33
ADS Sensitivity Transition Timing - Instant
Mouse Acceleration/Filter are both at 0, and Mouse Smoothing is Disabled
Field of View - 100
ADS Field of View - Independent