Why I die with one hit?

Hey guys,
So I’m playing Necromancer with the LOD Singularity build and I have every item as Ancient and I’m Paragon 750. My only problem is that I die with ONE hit , literately a single hit kills me,be it a touch of the poison on the ground,laser or a cold in the floor.
I mean this build is pretty good with damage and I got to 90 GR Solo but is it normal to die with one hit with this build?
Could you give me some tips on how i can survive in the game?
Link for my hero
Would appreciate some help .Thanks

Do not use Amulet Squirt’s Necklace.
While not taking damage, damage dealt is increased by up to 100% and damage taken is increased by up to 50%.

Belt Dayntee’s Binding - use any curse
You gain an additional 45% damage reduction when there is an enemy afflicted by any of your curses. [40 - 50]%

Gloves Stone Gauntlets
Getting hit increases your armor by 50%, but reduces your movement speed by 15% and attack speed by 20%. This effect stacks up to 5 times.

Boots Ice Climbers - you need it if you use Gloves Stone Gauntlets
Gain immunity to Freeze and Immobilize effects.

Ring Lornelle’s Sunstone
Your damage reduction is increased by 0.89% for every 1% Life you are missing. [0.75 - 0.95]%

or Rings Unity
All damage taken is split between wearers of this item

My equipment is here

These are all the toughness layers that I use:
In my setup I have both razeths volition and aquila cuirass so I get the 50% damage reduction at all times. Dayntee’s binding is also a must have for toughness, and I have aura of frailty to activate it. And lastly a unity ring combined with one on my templar, as well as the relic that makes him unkillable. I still don’t use the ice climbers - stone gauntlets combo cause I don’t feel I need it. Bone armor is another mitigation here. Everything is ancient, and I have decent rolls on my gear, meaning armor wherever I can get it, secondary resistances,etc… My max health is close to 1 million. I feel comfortable farming 100-110 rifts. All my other items are the typical lod mages gear that you can find in most guides.

Still, with this build you cannot face - tank stuff that other builds can and you have to be more mobile and watch all those projectiles coming at you. Also a lot of the survivibilty of this build , comes from the fact that you kill everything before it touches you, at least when you are doing speed GRs and not high pushing.