Autoguns probably aren't necessary when you already have a big, slow, high damage weapon, yeah..

As for the new guns, the Catalyzer and Pulsar.. hmm.. for the most part I'd say the Catalyzers are mostly good as a primary weapon... or if you want to have something that is both a gun and a bomb. Though it does combo remarkably well with freeze weapons like the Glacius, but since you don't have one of those, eh. Of course, you could get the toxic variant if you want to poison some things.

Pulsar is good for making sure far away enemies STAY far away, because once the shots have travelled half their length they not only do more damage and splash, they also push enemies around a bit. If you're really feeling the desire to inflict shock or smash gunpuppies you could go for the variant there. Also kind of amusing is that the shots explode if they reach their maximum range without hitting anything, so you can actually blast dodgy enemies by spreading the shots around a bit and firing from the maximum range.

If you want a gun for FSC/Undead stratums, but generally useless outside of those then go with Argent Peacemaker. The two-types split damage is a terrible thing, each gun of antigua line deals only 87% of its maximum to 2 groups, and a little above and a little below half of the maximum to the rest species, for Argent Peacemaker the 2 groups are Fiends and Undead, for Sentenza it's Beast and Gremlin. There is now way you want to use AP against Devilites since they dodge like hell and you will take a lot of time to get some damage on them due to the nature of the gun (6 clip shot, each shot deals minor damage), Greavers, those you don't want to fight with a gun unless its an Magnus line gun but thats not something you are looking for. As for Sentenza, gremlins in Tier 3 get the shield and like to dodge even more so it gets much harder to get some hits on them. And for Beasts, generally each your shot near a wolver that doesn't hit him will trigger its teleportation in Tier 3, having someone in party who tries to shot them with a Sentenza is an absolute horror as Wolvers also can teleport when they are doing the attack animation so you can basically spawn an alpha wolver on your face for the mess damage you'd deal him. And the real use it gets from me is crystal cutting / block cleaning / switches at Roarmulus Twins, but thats only the utility not combat use.
On the other hand we have Valiance, thats a really great weapon, it has a 3 shot clip, each shot pushes the monster a little back, its easy to master 2shotting to not reload, damage is really fine for a gun that will deal the same damage to all monsters, the splash is pretty okay i would say, nothing outstanding though.
Also, status effects on guns are overrated, especially shock, its only useful on groups so if you really want an alchemer you can go with the Nova Driver, its got recently a boost - in the second part of Tier 2 i deal around 81 dmg to constructs, and my weapon is still only at lvl 6.