The mouse acceleration issue is that there's negative acceleration if you move the mouse too quickly. In other words your turn speed is effectively capped. The mouse polling rate seems to affect this maybe?
Either way a fix was found here: https://www.mouse-sensitivity.com/forum/topic/5005-anthem/
If we change GstInput.MouseSensitivity in the config from 40 to 1 and then change all the other sensitivity values accordingly then it almost completely removed the negative acceleration.
Hopefully this helps with fixing everything. Especially since this fix makes the in-game sensitivity sliders useless as 100% is way too low, making it so you can only change sensitivity via config.
Edit: This only fixes sensitivity in fort tarsis. Once you're in a javelin mouse acceleration or smoothing comes back though not as bad as without the fix.
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