Necro is a heavy support role. You will need direct damage from somewhere else.
But You get great healing, debuff and damage buff from it.
Necro and warfare go well together as warfare will boost necro physical damage. Also high physical damage in General means You break shield faster for your debuffs.
Necro + geo can be seen as a dedicated undead healer support. Not just that You will have good heal from blood and poison but The physical armor spells in both trees will protect You from hydro healing spells.
