Ah, you're using Rathpith+Rainbowstrides with Rumi's for max block/spellblock. That will limit your ES. It's crazy strong, however, and not worth changing IMO.
Smackababy... is so wrong on nearly everything it's painful.
You should get a Vinktar's ASAP. If you can't get the phys conversion (most expensive), get the lightning pen one (cheapest) and replace Increase Crits with Phys to Lightning (you're running 2). Also, your shield (minus the block) is easily upgradable with ES, spell damage, and spell crit. And, work towards replacing Atziri's with a Taste of Hate.
And, do your uber. Master Herbalist will increase your single target. I'd also argue Veteran Bowyer is better than Nature's Boom. On long fights, just swap your Quicksilver for Overflowing Chalice and you should be fine.
And, if you don't need the resist on the chest, you're better off spamming 150 chaos on that to hit 750+ ES than buying something else.
You'll probably also get rocked to stun. Skyforth is the ideal solution, but Eye of Chayula ammy is fine.
As far as your tree, you shouldn't need strength and should go through Written in Blood ES / Mana rather than the intelligence node and the big strength.
And, I believe Eleron 7 increased Energy Shield on the amulet will be way better than flat ES craft.
AND, your flasks are disgustingly bad. You have no freeze and no shock. How did you make it past Merc Act 3?
There's no upgrade to Rathpith + Rumi's, nothing else will keep him alive that well. Definitely will want a Vinktar's ASAP, shit is retarded OP.
Definitely do Uber. You don't really have good poison scaling in the tree but it's still the best damage boost available.
Stun definitely is a big issue, but chayula is a huge damage loss (no crit multi). Get a Valyrium ring instead. Your other ring, replace the Ventors with a good Diamond or resist base. Get an ES prefix in there.
Get an amulet with strength if you need strength and pick up the 2 life/ES nodes to Written in Blood instead of the 10 int and the 30str nodes, that part I agree with.
He has an antifreeze flask (quicksilver). Shock removal isn't a big deal until he gets Vinktar.
Other than critiquing smack's critique...
Your belt has a WED craft. This does literally nothing for you. Unfortunately there's not really much better to replace it with. Eventually you'll want to upgrade this belt for more resists/str or replace the str roll with flask duration suffix.
Get some GCPs and quality up your blade vortex, bare minimum. You're missing 6% increased AoE by not having 20q.
But by far the biggest problem I see is just stun immunity. Get the Valyrium ring, upgrade other gear to recap resists, you'll wonder how you ever played without it.