I feel like Hammerheads are fine. I recently tested them with and without converted hangar as part of a destroyer lineup alongside enforcers, sunders, and manticores. Pretty much everything other than the Manticores did similarly, trading off positions, while the Manticore's missiles put them consistently above the rest (the Sunders did not do as well as I expected, maybe because things were too crowded? Not sure). The Hammerheads did best as frontline 700 range (+ ITU) units with mortars and needlers, swapping to mortar + HAC vs ordos. (Yes, I kept using them in this role up to Ordos, with a converted Hangar broadsword each: they did fine.).
One thing about the current Hammerhead: it is the easiest destroyer to build something functional with. We can argue about whether, when built precisely and compared to other highly optimized builds it stacks up, but the fact is that if a player just throws some guns and vents on, the thing will work well enough. Mortars, HACs, Arbalests, Thumpers, light autocanons, light assault guns, etc etc etc: the recoil reduction on the mediums and arcs on the smalls means that every gun will do fine (except maybe light mortars in the front smalls? Might be too high recoil there!). The system works with everything too. Medium stats with the only weakness being the rear + some guns = something that can contribute.