One of the things I miss most about the old Rainbow Six games was that they didn't pamper gamers with allowing you to carry multiple weapons into a mission. You had to strategically select your weapon after considering what the mission requires and what you plan to do during the mission. This added a layer of tactical depth because not equipping yourself properly meant a much higher probability of death and mission failure. Raven Shield did this the best. If you needed a bit more firepower than a standard pistol provided you could equip instead a small machine pistol. They're not much larger than a standard pistol and the magazines are small and light like a standard pistol mag. It makes SENSE.
This makes much more sense from a realism standpoint as well. Think about it, in Vegas and Vegas 2 you could carry around a M249, a PSG-1, and a Desert Eagle. Aside from how large, heavy, and clunky those weapons are (yet suffering no ill effects) you also have to consider the ammunition for those weapons. Ammo belts are freaking heavy (even 5.56), you also have the sniper rifle ammo, and somehow the magical ever replenishing infinite pistol ammo.
It's pampering the player. Make the player decide whether they want to carry a specialized weapon like a sniper rifle or take the safer all around weapons like assault rifles. Allowing them to have both removes the basic thought process of gearing up specifically for the mission.
...bah, who am I kidding. We'll get dual primaries again.