Out here on this one, but I miss vanilla havoc witchblade gunner, so here we go:
Phasebreaker has yet to find a home in a well performing build. Damage is still lowish, and it has only general support (but not +1 for the obvious gun class, which is fine because purifier has a million options)
Horns of Korvaak does see some niche use. Fits great with occultist secondary with chaos and vit conversion, gives +1 all in this witchblade scenario. Built in RR is the weakest type and on witchblade (single RR) it’s not going to do wonders, but it’s still a nice proc
Conduit of Eldritch Whispers is basically going to be required to get the extra 15% elemental RR. Due to resist profiles often being high across all elements, I’ve had extremely low success rate with end game elemental builds that have single class RR.
From there, gear gets very dicey. Elemental cadence has the booby prize chest compared to fateweaver, you get boots, and then pants are either elemental cadence or kuba for deadly momentum. Relic is serenity or plunder’s as nothing class specific fits, which is understandable.
Example gear layout (this is tactician but most of the gear ends up the same and has few occultist support skill options) https://www.grimtools.com/calc/RZRwWPPN. This tactician also fails to do end game (SR75-76) or crucible as damage is just too low/inconsistent.
This is probably outside the realm of realistic without a new dedicated set, but seeing some elemental cadence gear with +solael witchfire, +second rite, +deadly momentum, and +elemental% to one of the capstones (possession please) would make a huge difference. WPS will still be light but doesn’t matter as much with cadence. Phasebreaker seems like the home for some of these changes, and going soldier and/or occultist focus with it would prevent any purifier shenanigans but still help tactician as well. Basically the Scion of Arcane Force treatment
edit: example doodle, been awhile since I’ve tested so I’ll give this a go in the next day https://www.grimtools.com/calc/mN49p9Q2