We played a game where my friend's 10 Hammerheads took on my Avenger +boarding parties ISD, a Quasar with Interceptors, a Gozanti and an Arquitens fleet. He wiped me out but with huge losses, seven out of ten Hammerheads destroyed. I would have done more damage had I gone for my alternate fighter wing of Defenders.

I think a Hammerhead swarm is a viable build and can win but on that showing it's vulnerable to heavy losses whilst doing so.