Basically, there is undefeatable mouse smoothing in the game's input system. I will try to describe it as simply as I can. In the simplest terms, that there is mouse smoothing particularly means, that your mouse input is not directly translated into your viewing direction changing. Rather it gets processed, so that it feels sluggish compared to games, that support raw input, which is basically every other game. More precise explanations of how mouse smoothing works will probably just deter the person reviewing this report from taking it seriously or even forward it to a software engineer, so I will not give one.
Recently, I did this post regarding the same problem and related worse problems in Arma Reforger. It has been ignored. Probably the person reviewing it did not understand what I was describing and/or thought that the problem lies on my end, since there are not many people complaining about it. That there are not many people complaining about it, is probably because those who do notice it are those who would not start playing the game in the first place because of it and never care to create a bug report or support those who already did. I am creating these bug reports, because I play (over 4000h) and love Arma 3, which does not have this problem. And there are people complaining about it. They are used to the game's input feeling raw and direct, so they typically try to disable the smoothing, don't get it to work on their own, google it, don't find a solution that way and then (rarely) create reports on the feedback tracker or reddit. Then they leave the game because of the horrible feeling. These are just some of the reports I came across: