As a person who almost can't play any 3D first-perspective (shooter, action) games due to serious motion sickness, I'd say a slower cursor doesn't really make much difference. If you're not used to it (due to being different from your desktop environment), it probably would make it worse.

To me, the biggest factors to (worse) sickness are

1. Narrow FOV: usually the bigger the FOV, the better. But when it starts to have too much of "fisheye" effect, it can be detrimental.

2. How "fluent" your character moves -- if you have to stop/decelerate constantly (for any reason: interact with objects, clash with walls, sharp turns), it induces sickness very quickly.

Third perspective games are typically much better, but if it's in a confined space (like in a room) for extended time, it's as bad as FPS.

The best FPS I've played in term of having close to no motion sickness is Overwatch. Apex Legends is pretty good in this regard too.

Any Valve title is a vomit festa.