Again, the main issue with Doppelganger Blast is that you need to be as close to your target’s hitbox as possible to get the most damage out of it.
And that’s usually done by standing on your target.
That’s generally not a good idea. Really not a good idea for Beast.
If anything, DoppelBlast is more useful for Hell Mode or farming, places where the shorter cooldown gives you more options when going from room-to-room.
I did some limited testing in Bloody Lane between Doppel Blast and Dragon’s Fury.
What I found is that having more frequent uses of the skill was great, but having to run into the mobs to first set the Doppels and then to detonate them was a lot slower than I thought it would be.
With Dragon’s Fury I could fire it from the entrance of the room (or a few steps in) and land in the middle of the cleared room and run immediately to the next one.
Damage wise though it doesn’t matter. They both do the same amount of damage in the same period of time, so if that’s the factor you’re looking for, then it’s just a matter of preference.