Crate of Entertainment Killer?

So I’m working on a way to kill this POS. I came up with a single target high recovery build as follows.

https://www.grimtools.com/calc/aZqOoRm2

I’ve minimized any AoE effects to keep the boxes from splitting, and tried to maximize the time I can stand and Drain Essence him standing in a couple of seals with a Mark on him.

The Syphon Souls is purely for getting through the prior parts of the map to get to him. I don’t plan on putting skills into the AoE devotions for the crate fight, but I still need them for the bonuses.

Any thoughts on how good/ bad this might be to anyone who’s actually killed him yet? I’d like to start farming him, but those boxes are brutal.