The Problem:
Like in Arma 2 and possibly older games (I have not played those) as well as partially in DayZ, the camera rotation speed is smoothed, limited and bound to the mouse sensitivity setting. I demonstrated it in this video.
This has been addressed many times in the Bug Reports for DayZ, so because I am afraid this will not be fixed, I have carefully written down all that I have to say to this. These are the bug reports I could find that address this issue:

Report 1
Report 2
Report 3
Report 4
Report 5
Report 6

Test Methodology:
To test for mouse processing, I memorized the direction where I was looking in the beginning and slowly moved the mouse horizontally from the left to the right side of my mousepad. Then I memorized the direction I was looking and moved the mouse back to the original position very fast.

Normally, I set it up so that the character turns around ~ 5/4 rotations when I mouse is moved horizontally across the whole mousepad once.
In the Video, I test the following settings to roughly achieve this sensitivity:

Test 1:
DPI: 3400
Windows mouse sensitivity: 3
Arma Reforger mouse sensitivity: 24%

Test 2:
DPI: 1750
Windows mouse sensitivity: 4
Arma Reforger mouse sensitivity: 13%

Test 3:
DPI: 400
Windows mouse sensitivity: 10
Arma Reforger mouse sensitivity: 133%

Test 4:
DPI: 200
Windows mouse sensitivity: 15
Arma Reforger mouse sensitivity: 200% (still too low)

Test Results:

1. With every configuration, the camera did not rotate back to the direction it was looking while moving the mouse back very fast, hence the camera rotation speed is limited.

2. The higher one sets the mouse sensitivity setting in Arma Reforger, the higher the maximum camera rotation speed is. By that follows, that the higher one sets the DPI and/or the windows mouse sensitivity, the lower the effective maximum camera rotation speed is. That is because the game does not use the direct mouse input, hence the in-game sensitivity is determined by the product of the DPI and the windows mouse sensitivity. I have no idea why one should implement it this way. It very likely is not obvious to most users, hence creating an unfair advantage for those who know and use a low DPI setting/ windows mouse sensitivity to get an advantage.

Conclusion:
Limiting the camera rotation speed in a game does not only make it harder for the player to aim, it also prevents him from building up muscle memory or even makes him unlearn muscle memory he built up playing games that do not have such limitations/smoothing implemented.

The problem with muscle-memory:
Basically, when you play a (not necessarily competitive) shooter like Counter Strike, where you regularly make mouse movements that rotate the camera far, you memorize how far you have to move your mouse to look at the desired direction. When you play Arma Reforger, because there is a camera rotation speed limitation, you will consistently have to move the mouse further in order to look at the desired direction, hence altering your muscle memory and preventing you from aiming correctly in other games as well as Arma Reforger.
Mouse smoothing is also preventing the player from building up muscle memory. You can think of it this way: The more direct/ unaltered/ quick the camera's response to the user's input is, the more consistent the game's feedback is, the easier it is for the user to build up muscle memory. Obviously, mouse smoothing makes the input indirect/ alters it/ makes it delayed, hence preventing the user from building up muscle memory.

The problem with realism:
I suspect these "features" (camera rotation speed limitation/ mouse smoothing) have been implemented in order to make the game more "realistic", because e.g. a person cannot precisely point a heavy weapon to a specific spot 180° behind in no time. If you think about it very light-minded, that may be the case, but there is an objectively better solution.

The problem with players coming from competitive shooters:
Since this is still an issue in Arma Reforger and DayZ. I suspect most of the developers at bohemia do neither seriously play competitive shooters nor pay particular attention to what those who do might think about the mouse input processing. I think you should be more open to what others think about it.

Solution:
Other games like Arma 3, PUBG, every modern Battlefield game, etc ... do not have any mouse smoothing or camera rotation speed limitation for infantry gameplay, but they use other methods to achieve realistic weapon handling/ character movement:

1. character turn speed limitation/smoothing (PUBG, DayZ, Battlefield, ...)
2. weapon turn speed limitation/smoothing (PUBG, DayZ, Arma 3, ...)
3. turret turn speed limitation/smoothing (Arma 3, Battlefield, ...)

So the solution is: implement all of the three turn speed limitations and smoothings and remove the camera rotation speed limitation and smoothing. Basically, by this, the problem with muscle memory is solved while the game stays realistic.
As far as I can tell, the weapon turn speed smoothing and turret turn speed limitation and smoothing are already implemented, but not tuned enough. If you turn up the sensitivity to 200% and turn as fast as possible when aiming down sights as infantry, you can see that there is no weapon turn speed limitation at the moment.

Other thoughts:
In my opinion, the infantry weapon-handling in Arma 3 is perfect and should be built upon in Arma Reforger. There is no camera rotation speed limitation, and there is a very well tuned weapon-specific infantry weapon turn speed limitation/ smoothing. That is probably why I spent 4000 hours playing Arma 3.
On the other hand, there are also problems with the camera in Arma 3. There is a camera rotation speed limitation and a different mouse sensitivity for helicopters, planes and stationary weapons, and there is no character rotation speed limitation. Those are things, that should be avoided in the development of Arma Reforger.