I generally try to stay out of these things as I don't usually have the time to dedicate to an ongoing debate. I've had a little time on my hands today and the more I've thought about it, the more I've thought some things should be addressed. I'll speak from my experience and FYI if for nothing else. Given that mouse speeds can be changed on the fly and .ini files tweaked, the whole concept of reduced mouse speeds when resting is moot anyway. Never the less, I'll explain why (in a perfect world where game mechanics are played as intended) I like the reduced speed of the mouse when the weapon is rested and the concept behind it.
To avoid a message that warrants a tl;dnr, and being too over the top, I'll dispense with my life experiences for qualification and just tell you that I still shoot some type of firearm daily and have for more than a few decades.
One rests one's weapon against something to steady it. By definition in doing so, one is trying to limit the amount of movement introduced to the sight picture from extraneous forces (anotomical, positional, environmental, etc.). Several things happen when one rests and holds their weapon against that rest. We are basically concerned with two. Range of motion and speed of movement.
When one is no longer free standing but has their weapon rested against an object (tree, wall, window frame) their range of motion is limited within the stance they are in. If one needs to follow a target outside that range of motion, naturally they need to reposition themselves. And though they may leave the weapon against the object, the usefullness of the rest is voided. So range of motion while rested is limited.
When using a rest for the weapon, one is intentionally trying to steady and slow the relative movement of their weapon's sight picture to provide a more accurate shot. Otherwise there would be no need to bother with the rest. If one chooses to move their weapon at the same speed at which they do 'free standing', then the benefit of the rest is lost. So go ahead and shoot 'free standing'. You dont' need the rest. An 'exaggerated' movement of the mouse for a minute change in the sight picture works quite intuitively and quite well for simulating the 'effort' used to precisely bring the sight to target while resting the weapon against something.
Though it is not perfect and I'll be the first to admit that the system could use a tweak or two, I still think the system as it is emulates shooting from a rest pretty well and is quite natural in its implementation. The relative speed/response of sight changes and the relative range of your target acquisition should be less than that of your free standing posture.
In a perfect gaming world, we would all use the same mouse speed and issues such as this would not come up. Unfortunately we don't and therein lies the delimma. There is no doubt that the current system "favors" those playing with the "default" mouse speeds that the developers had in mind over those that play with reduced mouse speeds. (At the risk of being verbally abused) it would seem to me that those playing with reduced speeds 'want to have their cake and eat it too'. In other words, they want the best of both worlds.
I don't have a 'correct' answer other than to say that I'm comfortable letting TW put into place the system they find best suits their game concept. From my experience, and imho, the current system translates weapon resting well. Again, as I mentioned at the outset, with dpi mouse changes, ini changes, etc., its all moot anyway. Even so, I don't advocate changing an intentional game design just because it can be circumvented. If others are doing it and one feels they must keep up with the Jones' then they should do whatever they feel comfortable with. (They're going to anyway...)
"And thats all I have to say about that." Forrest Gump