Smoke Cans just aren't effective enough. When I toss 3 canisters, and stand on opposite sides from the enemy from the smoke, there's no way I should be getting pounded on from an enemy at equal level to the smoke. It should be a visual wall.
I'm not saying that you couldn't blind fire through the smoke and hit something (if you remembered where they were), but still. It's like the human's can't see squat, but the aliens come with ultravision. Yes, this is on the HARD/VH levels, so they should get some advantage... but I personally think the 8:1 damage ratio difference should be enough of an edge if we're not going to do AI manipulations.