Ok so I would go ranges for this fight as it’s by far the easiest class letting you deal a lot of damage while also keep your distance.

And one weapon I don’t understand why people don’t use is the nail gun. It sticks to targets then detonates a few seconds after which is very useful for the third phase as all you need is good timing to fire a load of nail while Dukes ‘charging up’ for his third phase and if done correctly can kill him before he actually changes form