One of the biggest problems was that that sort of thing didn't affect people as much as it should. There were longrifles with thermal scopes, the DMR could be used while you were using NVGs, and of course cheating bastards could just turn their gamma all the way up. Smoke grenades existed, but weren't reliable finds, and didn't cover much area anyhow. You'd need to know exactly where the sniper was (assuming they weren't with others), and you'd still have to poke out from cover to place the grenade somewhere that would allow you to run directly away.
Granted, a lot of snipers in the mod were idiots who couldn't aim for shit, but with a 1-2 hit kill weapon even a moron will get lucky eventually. That, and pretty much all of the longrifles were either obscenely overpowered (DMR, AS-50, the one with the thermal scope) or had automatic zeroing. You didn't even need a rangefinder or the ability to eyeball distances, because the map lets you drop a waypoint that gives you the exact distance from you to it. It didn't help that a lot of them preyed on new players who couldn't effectively avoid fire, take cover, or know common sniper locations.
In ArmA, mortars and HMGs are squad weapons that require multiple people to carry (and even then, running too much with part of one will exhaust you), and even MMGs are squad-served, in that you've got the gunner, the spotter/guard, and the ammo mule. The closest you'd get would be an assault rifle with an UBL (which, to be fair, are pretty OP themselves in the right hands), but the problems with that are: it takes a pretty good player to accurately place rifle grenades at any sort of range, and it still requires you to peek out of cover.
The most effective way to deal with snipers is and always has been to wait for one to start killing new spawns, flank around and kill them, take their rifle, and counter-snipe the ones that aren't douches and terrible shots. Which sucks, because it just perpetuates that sort of gameplay. The only times you get interesting gunfights in the mod are when everyone involved is a relatively fresh spawn and the best weapons present are the ARs and such you can find in the Electro fire stations.