Hi there,
is really like grim dawn and i used the following damage types by now:
fire (LMB firestrike)
lightning (LMB savagery/primal strike)
physical (LMB cadence)
ice (LMB amarasta bladeburst)
bleed (LMB bladearc)
elemental (LMB Panetti Missile)
poison (LMB not transmuted dreegs evil eye)
So there are other damage types where i dont know
what LMB skill i can use for a build:
vitality
chaos
aether
pierce
So which LMB-skill would you use for there types? 
I did an Aether Firestrike personally using Aether of Soul and some conversion.
Also I can easily see a Cadence Chaos (Obsidian Juggernaut in mind)
you can bind most of the attack skills to LMB, even if with cooldown. most of my physical builds use Oleron’s Might.
Someone did Chaos Cadence with the Harbinger set. Was pretty strong.
On topic:
Vitality: Vitality Phantasmal Blades. Dreeg’s Evil Eye focusing on Vile Eruption.
Aether: Panetti’s or Callidor’s Tempest. Albrecht’s Aether Ray can’t be assigned to LMB I think but it’s also an option. Obsidian Tremors via Obsidian Juggernaut and Chaos to Aether conversion.
Chaos: Obsidian Tremors via Obsidian Juggernaut. Fire Strike via Brimstone and Fire to Chaos conversion. Aether Ray with the transmuter is also an option here again. Could also try BWC with Demon Fire and Element to Chaos conversion I guess?
Pierce: Pierce Cadence with Valdun’s Treachery or Dermapteran Slicers (Sword and Board or Dual Wield). Shadow Strike with Execution/Amarasta’s Quick Cut.
You can use converted phantasmal blades for either Cold, Vitality or Chaos LMB attacks. The pierce dmg sadly gets lost.
My lightning caster Druid still using Empowered Lightning Nova bound to LMB. He might need some updating but the nova was obliterating everything near him a few patches ago and the cast rate was high enough it kept the devotion procs rolling non-stop.