That great for you at cap, and not uncommon in non-reaper. However, in Heroics and early Epics, DW has always been a problem for DC casters. Especially when it can not be dispelled and the mob very likely has immunities to other damage types.
Remember, the game isn't just about you or me at cap, with our past-lifes and tailored gear, but about everyone else's experience.
The OP wants to build a Pale Master, and switch from negative energy to force to bypass immunities....
But Deathward Does NOT stop negative energy damage, despite what the description says.. It stops level drain, ability damage, etc.
Did you know that in this game, there are more mobs immune to fire or cold spells then negative energy?
Unholy Avatar makes undead VULNERABLE to negative energy, which means the 2nd hit they take gives extra damage (purple numbers).
About 50% of the monsters in the game (including raid bosses) take extra damage from negative energy.
In fact, I can only recall two types of monsters that are actually immune to Neg Energy - Scarecrows and Golems... There might be a couple more types, but they are very few and unremarkable...
Linking Dranconic Incarnation mantle to neg energy is a wise move.. With the hordes of undead in the game, you can shoot say Chain lightning, hit all the mobs, wait 1 second for the first dot tick, then necrotic blast and they are all dead! If not, wait for the 2nd tick...
In heroics,
I think you can get Unholy Avatar by level 5 (required Wiz lv 4 and 20 points spent), So at that point you can kill almost anything with necrotic bolt.
From level 5-12 there is a little struggle to level a PM, but that's the level range where you use other spells like Ice Storm, Acid Blast etc.
From level 12 onwards, you're laughing with a PM.... Necrotic Blast wastes pretty much everything in 1 shot and it's a tasty AOE with huge spread (more than a fireball) and only costs 5sp to use.
Necrotic Ray and Rend the Soul = 1 shot to any reaper.
And for those pesky scarecrows you can use chain lightning, firewall to clear them, and Golems hit them with cold or acid - until you get Arcane Tempest and that will absolutely melt the 2-3 mob types in the game that are actually immune to your Neg Energy..
And if you want to be a DC Caster, then put up with the DW, or like I said, invest heavily into PM and Negative Energy spell power and you'll be fine!