Light for the Necromancer.

Considering that you need to upgrade a Necromancer in general, some defense is essential, especially against the Stronghold. Otherwise, they will simply tear you apart. According to your logic, if the Stronghold has an excellent attack, then nothing needs to be done to counter it. And this only worsens the situation. Let's say you don't have any defense. And they have a high attack and a corresponding skill. That is, +15% to attack. And luck, of course. And with luck, as is known, all attack bonuses expressed as percentages are doubled... In short, if you don't upgrade your defense, nothing will remain of your army, and you won't have time to cast any spells effectively. Moreover, Vengeance will not be so effective, as Fury will absorb a significant portion of the damage.
So, unconventional builds are certainly good, but not in this case (IMHO).