[Taqwus]

Ermor also still needs gold for those labs, temples and castles (unless it wants to be casting the Wizard Tower ritual, and that's not all that cheap if memory serves), yet will rapidly lack the taxpayers.

The sacred units are also either expensive (Wailing Ladies cost 15 death gems each and there's no multiple-Lady summons even if you could afford it; Soul Gate can get them free, but this seems VERY rare) or not that great (KoTUS, which are fragile and never heal, and can only be gained through auto-reanimation by Ashen Empire at a fortress).

The mages aren't that versatile either; until Conj 6 or so is available (spectres) it's basically Dusk Elder only for a random, and a single point at that, for 20 death gems -- two turn's worth (at normal richness) of gem income from the Unholy Sepulchre.

Death eventually has some great spells (Tartarian Gate comes to mind, albeit for best effect GoR is needed and that requires Nature-4 plus 20 gems; Ghost Riders is also a good backfield temple-smashing spell; Well of Misery might be second only to Astral Nexus in gem-producing spells) but still, it takes work and a Solar Brilliance or use of the Ark or Wrathful Skies could really ruin the day of even a rather large undead horde.