Yeah but he sends them 100 at a time. To take on serious PD defence you need to spam fleets at the one time and I've not seen Hieruf do that. I will lose some planets I'm sure, after all I'm only logging in once every few days, but I just don't see him making a real impact against my core production areas.
Dunno..he has sent like 10 such fleets at one of my planets and they've arrived pretty closely together. He's starting to do that at a few other locations as well.