The more I look into Acid damage, the more I think it needs to be buffed to some degree. There are soooo many creatures that our outright immune to it: Gill Men, Lobstermen (10%, but basically immune), Tasoth and the guardian form, Calcinites, Deep Ones, Tentaculats, Xarquid, and I think also the Triscene. So, any sort of creature that has high armor, where these kinds of weapons would actually be useful, but it doesn't work. What is it useful against?
Aquatoids and Jellymen? Who cares? They die to anything.
Naga and Carcharodon? That's okay, but it's too situational. Naga typically die from one hit of a Gauss Rifle, anyway.
Freaks? You still need to get past the MC shield, and then they die in one hit.
Hellcrabs? Yeah, that's useful, but again, why am carrying Acid Guns around just for a few creature types?
Worse, it's not like these guns are weak against the other types. They are completely immune. You don't see that with Gauss at all. Gauss Rifles are good all-purpose guns. Or any of the other guns, for that matter. They can at least do a little bit of damage against creatures that are strong against that damage type.