I know I may get some flack for this and people will just tell me to play better and get better gear, but I honestly think there are some flaws regarding Vanaduke that put him into the realm of artificially difficult. There are two instances where the boss is just too crazy. I'll note each one and how I think it should be changed.
1) The ceiling falls too quickly. Now I know that before the ceiling falls there's some light on the ground, but the time it gives you is not enough if you're in reloading your gun or finishing up a charge attack or whatever. I think either the time it takes for the ceiling to fall should be increased slightly or Vanaduke himself should make the ceiling fall less often. Maybe give him a standard attack to use so he doesn't smash the ground all the time to cause the ceiling to seemly fall constantly.
2) When it goes into the 2D shooter mode. There's 2 problems that I think could be fixed to make this more manageable. The first would be to make it so that the orbs don't light you on fire. There's already enough fire at this boss fight as is. So it would be nice if the one thing that isn't fire didn't deal fire to you. The second is that when there are orbs flying all over the place it can be hard to hit the mask. One suggestion for this could be to make water go through the orbs so that you're not constantly struggling to just try to hit the mask with water to make it vulnerable.
I've played Vanaduke a few times since after the rebalance, and each time it seems that multiple people spend hundreds of energy. I just finished a failed attempt where everyone spent around 300-500 energy each. You shouldn't need to do that to beat a boss.
Vannadukes is a hard guy I agree with that, but I only beat him two times out of about 20 or so attempts, but each time I got close or even beaten him it was due to the team I was with. You need a great team and a lot of teamwork to beat him. The two times I beat him I used less than 300 energy on revivals. My team was smart we all had jobs, and we would do them, and you need the right gear (Fire resistant armor etc.).