In my heart he will always be the usurper but yeah you are right.
Death should be a MAJOR threat, not the poorly supported faction it has been til Now.
Hope the new tome will change something... but Death needs also new models
To be honest, they'd better introduce some new proper factions with those models. The Death grand Alliance completly and utterly owning allegiance to Nagash means Nagash should easily be able to conquer everything. The only ones that might stand a realistic change against
literally every single dead thing across all realms ever*. Would be the seraphon, as our slann can conjure up similar numbers from memory while maintaning the required order to actually fight such a massive front. Plus, I'm guessing the conjured seraphon won't leave a corpse or soul for Nagash to claim, which would mean Nagash might actually run out of corpses/souls at one point, and even that would require the slann to figure out a way to stop nagash from raising the same souls/corpses over and over. Hell not even the various factions of chaos stand a chance without properly unifying seeing as Nagash never actually
needs to fight them. If Nagash simply murders everyone in Order and Destruction there's noone to sustain chaos, no emotions of rage for Khorne, no scheming for Tzeentch, no circle of life for Nurgle no freaky stuff for Slaanesh, and the horned rat probably won't survive without the believe from his skaven either...
Death's fluff has become rather scary with that those few throwaway sentences of Nagash controlling
literally every single dead thing across all realms ever *. It's rather absurd compared to the other grand alliances that at least have some internal struggles. Hell, how would they even set up a break away Death faction, giving it multiple Nagash-like beings in a state of constant battle vying for whatever souls they can get? So sort of a ripoff of chaos but with more skulls (heh.. more skulls than chaos, as if they don't have enough of em...). Unless there's something preventing Nagash from raising the same souls over and over he should be nigh unstoppable, and even if he can't all he needs to do is wait several millenia and then just venture forth with an army consisting of millenia worth of death from every single other faction. Hell, just throwing them at the enemy in a large pile would be enough to destroy any and all resistance by sheer weight of numbers...
* with the exception of SCE cuz apparently Sigmar can cheat the defacto god of death, how exactly did Sigmar lose his first wars if he is that powerfull anyway? What kind of incapable general is he?