Can somebody give me a quick run down on how to play the nurgle spearhead? The model count is relatively low and the plaguebearers and leader die pretty easy.

I'm not exaclty sure what they're supposed to do since the leader is useless without nearby plaguebearers to boost but they're both squishy, and the blocking them up with the blightkings seems like a redundancy that just sacrifices board control.