You are quite wrong when you say that the suppression does nothing not only does it help a lot with ranged, it also means I can one hit pretty much every character in the game with a power attack, because it normally takes about 2 heavy hits to kill an Ork from behind with the scream it takes one.

It doesn't really seem to help if a deff gun or heavy bolter is aiming at you though, you charge them with the suppression but they can most of the time still kill you with their rate of fire.