Pestigors derive their use in a nurgle roster from their speed and having vanguard deployment. Which can be situarionally pretty useful. But in practise they're kind of an emergency recruitment serving as somewhere between cavalry and infantry. They're great in the beastmen roster, being a pretty hard hitting frontliner in a roster truly starving for that.

Plaguebringers are fine but mortal infantry is just so much better.

GUOs are Fun and thats a great value add. But they suffer from specialising in clearing out infantry tarpits with aoe damage, which as nurgle you wanna do with mortis engine effects and your own, stronger, tarpit. They also suffer from being deceptively fragile. They will die if a ranged unit sneezes too hard in their general direction.

Plague drones fill a role in your roster that few to no other unit does, flying glass cannon. You don't need a flying glass cannon, if you wanted that stuff you'd play Tzeentch. In my experience plague drones are only worth bringing to sieges, where their tendency to send units flying in an otherwise non damaging fashion results in massacres from fall damage. And even then I'd rather have a knight or a chaos warrior.

Soul grinders are ok.