I know I'm not going to make a lot of friends with this, but if you wanted less Blitz and Shiv, wouldn't it be worth considering an alternative to the flame orbs circling Vanaduke? After all, even expirenced players prefer to not get too cuddly with him, making almost all close-range weapons useless (for most players!).
I don't mean simply removing them, but replacing them with something.
For example, instead of circling him they could travel the room. Like this.
You see his eye pop out a 0:23? Now imagine that is is not an eyeball, but one of the flame orbs, bumping around the room. Having played that game I can assure you, two of those in a room the size of the Throne room with walking speed and you'll have your challange.
What this would mean for some of the weapons?
Shivermist - Freezing Vanaduke easily removes the almost every threat from Vanaduke. Even with his balls of (on) fire in phase 3 you can keep a save distance. Detaching them would make freezing him less important, as he himself has become a less of a threat. Also, you couldn't just idle around as the orbs are continually traversing the entire room, despite him being frozen to one spot.
Bltz/Plaque Needle - Running around with a charged Blitz makes you slower - slower than the traveling orbs. Add that to the fire tiles and slag guards and you'll see that it will become a lot more difficult to get a clean shot at Vanaduke.
Swords - With the orbs not protecting him directly it would become viable to attempt close combat.
Disclaimer: I myself am a gunner, but I find the current mechanics of this fight to be little fun and rather unfair at times. Also, I can see a lot of appeal in bringing close combat and movement into it.
I disagree with this concept due to a few major concerns with it.
One is that it wouldn't make the fight significantly fairer. One of the main difficulties of the fight when not using the Blitz or Shivermist (or even occasionally when using them) is the impact that the RNG plays on the fight, and how costly a small mistake can be: lava can spawn on top of you or directly in your path if you're not careful, Vanaduke and his guards can push you into a corner with no way out, or Vanaduke can decide to charge at inopportune moments as you're attempting to navigate through a small patch of lava.
The reason I believe this is important to note is that if the fireballs no longer circled around Vanaduke, it would add another random element to the fight that would be hard to predict without constant awareness, and would punish small mistakes. If this idea were implemented, I could see the Blitz + Shivermist combo being even more prevalent: not only would the fireballs no longer block Blitz Needle attacks on Vanaduke, but there would be extra incentive to finish the fight as quickly as possible so that none of the fireballs had any chance to cause issues.
Another concern is that this method could possibly lead to the Dread Venom Striker edging out over the Blitz Needle as the one centralizing weapon for the Vanaduke fight. The DVS is already extremely effective in Vanaduke's first phase and against his mask phases, and with these changes, it may lead to a new strategy arising of simply hugging Vanaduke, sidestepping the Slag Guards and fireballs when they rush past, and constantly spamming DVS.
It does seem like a decent idea and I agree that the fight would probably benefit from being changed, but I'm not sure this is the way to go about it.