I've been looking at this gun for awhile now and I'm thinking about getting it... Those green bullets are sure attractive.
Plus how is this gun compared to the other elemental guns. I have a Polaris and Magma Driver... But I'm getting bored of them. I don't have a valiance cuz I use Supernova for knockback. For piercers, I already have Blitz Needle and I don't use piercing guns so much. Also I seen party members using Riftlocker and looks like they are having a hard time chasing fiends and beasts with it.
How is the Arcana?
You mean that Proto Gun is similar in its mechanics to the Blaster line, of which Arcana is the elemental example? That much is true.
Arcana is going to do less damage than your Magma Driver, while also being more boring in its play style. It's going to do less knockback than your Polaris. But if you're tired of Magma and Polaris, then I agree that trying new things is a good idea. That's the fun of this game.
Speaking of which, have you sampled the Catalyzer, Magnus, and Antigua gun styles? You didn't mention them.