Snipers blow chunks in Helldivers 2, and here's why.
The Diligence does a pathetic 165 damage and basically isn't worth using, especially since it can't penetrate armor. It probably is similar to a 5.56 rifle which means it should be medium armor penetrating at least. It's literally outperformed by almost every other weapon in the game for either penetration, damage, or both.
The Diligence Counter Sniper does 200 damage, which is OK, but still pathetic. Penetrates medium armor, but is embarrassed by the fact that the Senator does the same 200 damage and penetrates heavy armor. I've got a news flash for Helldivers devs - there is no universe where a revolver does more penetration than a fucking sniper rifle. The Counter Sniper is probably a .50 BMG rifle or similar, and if I shoot a Charger or Hulk in the face, it should immediately sit right down on its ass. The Senator, since it fires a slower round, should be the one doing medium penetration.
The Eruptor is pay-to-win, since it's the only usable sniper rifle in the game, but it's crippled by short range(the round explodes after a short distance) - so why bother putting a sniper scope on it at all? It's the only rifle capable of clearing out medium bugs just fine, but not due to precise sniper shots - due to exploding rounds. The rounds bounce off Bile Titans unless you hit them juuuust right - but it can one-shot a Factory Strider from beneath(as it should). It's utterly incapable of damaging a Charger at all, unless for some reason the Charger is heading away from you.
Here's how sniper rifles should work: the recoil should be horrendous unless you're prone. The Diligence should penetrate medium armor. The Counter Sniper should penetrate heavy armor. The Eruptor should penetrate heavy armor, stun, and clear the surrounding area with the explosion. There is very little, if any, armor that we know of that can stop a .50 BMG, so there's basically no bug or bot that should be able to take Counter Sniper rounds or greater and keep walking.
Sniper rifles are meant to be slow firing, high damage weapons that reward precision, and penetrate effortlessly. I should be able to find a spot, see a long distance with the scope and ping for my team, and land shots in critical hit points at range and bring large enemies to their knees while my team is working on crowd control. Unfortunately, most of the sniper rifles in this game are fucking useless, because the devs feel like you're supposed to bring a rocket launcher instead of a precision rifle.
Signed, the teammate who wants to play as a sniper, but can't, because there are no good long range rifles in the game.
I also posted this rant to Steam Community if you want to discuss there.
The Diligence is a DMR (or SPR), it excels at accurate fire without losing too much in terms of ammo capacity and sustained rate of fire. Use it against bots, it is a surprisingly good chaff weapon and can take good care of devastators if you aim is true. Could you just use a Tenderiser instead? Yeah, probably.
The CS is something I never bothered with - I suppose it is a bit better suited for Devastators and maybe shooting the joints on a scout strider?
The Erupton is ... special. Why you classify it as a sniper rifle is beyond me, but you do you. I also wonder what you were expecting from a sniper rifle when shooting bugs - enemies that will quite easily overwhelm you with a combination of sheer numbers and armoured support (can't kill hunters if you need to dodge a Charger). The AMR will take good care of the medium weights, such as Brood/Alpha Commanders and Hive Guards and can still take on Hulks and Chargers in a pinch. No clue why you think that a rifle-calibre or intermediate cartridge should take out armoured units.