Most people are looking at this pragmatically, not how it fits in with the weapon's aesthetic. More to the point a piercing Antigua line gun would be essentially useless since regardless of speed pierce weak mods still dodge so it would be inferior to a Callahan.
The problem isn't a weapon being niche, it's when a 'niche' weapon is being outperformed at its own niche which makes it worthless. The peacemaker been a niche FSC gun would be fine if it wasn't for the fact Blitz Needle is superior in every way. Sentenza being a niche gremlin sniping tool would be fine, if it wasn't that the Umbra Driver and Biohazard are both currently better against gremlins. The Dread Venom Striker is fine for example because it does have a niche that it does better than other weapons, the peacemaker and sentenza are not fine because they don't have a 'niche' they're good at. The whole point of a weapon being niche is that it excells at that particular job, and the closest thing either of these guns have to a niche they aren't outperformed in is as Lockdown guns; which is a legitimate point but at the same time they won't actually be any worse at it if made pure-typed.
That's not to say the be all end all solution is making them pure typed weapons, but they absolutely need buffing in some capacity.
I can see where you guys are coming from for the base damage upgrade and keep split damage, but honestly, wouldn't you rather just have two separate guns? Especially with the new loadout stations, there's even less of a point to split damage. I would rather have a piercing antigua line for wolvers and fiends, and a shadow line for gremlins. Like I said in my earlier post, make Argent Peacemaker pure piercing and have an Undead damage bonus, and make Sentenza pure shadow with a Gremlin damage bonus. It would fit the descriptions while still having a very nice niche
Argent Peacemaker desc talks about "gunslinger priests" and "ushers for those who refuse to leave this world" which makes the Undead damage bonus, plus the fact that we are lacking in piercing guns, not to mention have no FAST piercing guns, we should make it piercing.
The reason Argent Peacemaker should NOT do elemental damage is because there is absolutly no reason why it should do well against constructs, and in fact, it should be weak against them. Think about it, contructs aren't affected by holiness because they cannot be affiliated with it, so the gun should treat it as such.
Sentenza desc talks about "contains the soul of a knight" and "wielded by an evil one" so it should do shadow damage, and since Gremlins are closest to a knight, it should get a Gremlin damage bonus or no bonus.
Sentenza shouldn't be piercing or elemental, because shadow damage fits it a whole lot better than the other two.
Do you see my point now? And if it's really needed, I'm sure the devs might be able to come up with a third line for elemental damage, and if not, I see no problem.