Just a few things I see off the top of my head:
You have very little in the way of +max life on your gear. Not sure you are resist capped either?. Those are the two glaring gear issues I see.
6 socket your axe, it will help your damage as the Molten Strike proc from the axe gains benefits from any socketed support gems. Doesn't have to be 6 linked, just the sockets.
As far as your build...I'm not really sure what to do with that pathing. It's definitely not efficient, drop some of those elemental damage nodes you are going for and take the axe stuff on the marauder side. That bottom part you have coming out of the scion start area can be completely respeced out and you can path from that big life wheel down into the duelist area for more damage nodes/life. Take Vaal Pact.
Oh, you might want to also drop Blood Pact. Not using Hatred and Herald of Ash is a pretty big DPS loss and you don't want those auras reserving your life. The duelist area has a life/mana leech cluster you can take for mana regen.
That said, have you considered going using Cyclone for your clear? You are basically a Ngamahu Cyclone build already, just drop molten strike from your links and use cyclone. The Molten Burst proc from the axe will basically act as your single target once you 6 socket it. It's been a while since I've played that build but a 5 link might be Cyclone-Melee Phys-Elemental Damage with Attacks-Phys to Lightning-Then either added fire, fortify or a Blue socket that you can put Increased AOE with a Conc effect gem to swap in for bosses.
Probably want to do your Merc lab soon, and I'm sure there is more you could do but that's just a start.