The Poxmakers of Nurgle, led by Ku’Gath Plaguefather, are a defensive, tanky faction. They have few missile units and none of those will trade well with ranged units from more missile-focused armies. They do have a ton of hitpoints and defense, as well as various healing abilities allowing them to soak up a lot of damage, but they are also very slow, giving the enemy plenty of time to deal out that damage. Nurgle magic is good, but not excellent. It’s a bit more expensive and a bit less effective than other lores of magic. So while Nurgle is amazing at taking on melee focused armies and just outlasting them, his factions are probably more vulnerable to ranged attacks and magic than any other race in the game. But they make up for this (somewhat) with a very fast recovery time