Camera movement on controller feels stiff and unnatural by default

[Constancies]

Describe the bug
After binding the right stick of a controller to look up, look down, turn left, and turn right, moving the camera feels slow, especially when moving it in a circular motion. It feels as though there is a strange acceleration curve to the camera for each axis that is activated, as though the stick was merely mapped to arrow keys on a keyboard (which could sort of be true?)

Your System
OS: SteamOS Holo 3.7, on the Steam Deck OLED
Version: Dhewm3 1.5.4 Flatpak

To Reproduce
Start a new game, open the pause menu, settings, and controls, bind the right stick of a controller to look up, look down, turn left, and turn right, and then try moving the camera around.

Expected and actual behavior
Expected: The camera should move smoothly and responsively like in other FPS games such as Doom 2016
Actual: If moving the camera to the right, and then up, as an example, the camera visibly slows down as it starts to move up.

Additional information
Here's a video of the expected behavior, achieved by mapping the right stick to mouse input with Steam Input:

good.mp4

Here's a video of the actual behavior, without any modifications to the controller layout:

bad.mp4

Log:

dhewm3log.txt