That's perfectly fine, you are a Nurgle Herald in a unit of PB's your job is to get shot at and survive.
End of the day a single breathe shot is never going to compensate for loosing around 200pts of models (Breathe Palanquin herald and say 7 PB's). Even if you do hit it is only 4's to wound which is ok.
If you want to have a breathe bomb then you have to take Flamers, end of. You get 3 Breathe templates for 105pts, almost the same as the Palanquin, Breathe Herald on his own. That means you get 3 times as many hits and suddenly wounding on 4's is not so mediocre.
Dropping a single Breathe template in close is never going to do a lot of damage (exclude a lot of luck) and then your Herald is going to get counter charged and die like a chump to the first lot of power weapons/fists that swing his way as he will be in combat too early and the tally won't have kicked in.
Field Marshall Lord Neil Alister Mackenzie Kerr the Marquess of Lothian
aka Team Scotland 40k Captain 2012