Most of the disadvantages of running a suppressor on a weapon are related to wear on the weapon and overheating, Arma 3 currently has no built in simulation of overheating. In real life firing a weapon with "hot" ammo out of a suppressed weapon will indeed slightly increase muzzle velocity, but its still going to be very loud. At best you're going from "gunshot" to "car backfiring"
Originally attaching a suppressor would magically make your gun act like it was loaded with subsonic rounds, which is what actually provides the decrease in damage and range video games associate with Suppressed weapons. This was removed because it was dumb for your ammo to magically change powder loading.
But it was only half done, so right now you have a situation where the ballistics of firing a hot load out of a suppressed weapon are done right, but the sound simulation isn't. But the problem is that if you do the sound simulation right, you're going to get a bunch of people either complaining because their suppressor "isn't working" or complaining because Subsonic rounds have crappy ballistic performance.