It could be a number of variables, are you using a hard pad vs them using a soft pad?
Some people are arm aimers vs wrist aimers, they may have a large pad and though the sensitivity is higher, they are making larger movements with arm aim rather than wrist aim which would have you hitting the turn speed cap or overshooting your targets.
This is why you should always use someone elses config as a baseline to finding YOUR preference. Lower the sensitivity until you are comfortable. I'd recommend that you watch the tutorial "How To Find The Perfect XIM Mouse Sensitivity Tutorial" from the XIM Gameplay channel.
https://www.youtube.com/watch?v=rs0sH4rfGRcThis will help you find your dexterity level, and don't be shocked if it feels much slower than what you thought it would be. I did this about a year after using XIM and it made a big difference, I've slowly raised my sensitivity since then as my dexterity has improved.
When you look at someone elses config you should be asking, why is this config better than the vanilla config? There is really limited answers on why because the vanilla ST (configuration with default settings) is trained to be 1:1.
1. Aim Assist: The vanilla ST will not account for aim assist as its intention is to provide a 1:1 look mechanic.
2. Turn speed: I've seen some configs to better deal with turn speed caps on games where it is low, this includes advanced in game settings, or ballistic curves with deceleration via the XIM.
I can't think of any other reason that a user config with any settings would be better than the default / vanilla ST provided by XIM, along with whatever in game settings that are required and listed on the XIM forums here:
https://community.xim.tech/index.php?topic=43775.0