Why Helstorm battery is spawned ? It should be available like helblaster or make it a special unit for Nuln only. It is rare choise as a helblaster in WFB and it is a mainstay in empires armoury(if the count have the money).

I can understand why warrior priests and wizards and engineers should be spawned they are powerful and veeeeryy rare and it is logical that Counts wouldn't be able to field such units en mass and if so they could do it only in times of some big crisis. But with helstorm battery it is as powerful as helblaster and if you can afford it to buy it well it is yours to use. At least that my understanding of warhammer lore.