Why would I pay 10 DP for a Hammerhead when I can pay 11 DP for the same kinetic firepower on a Shrike with CH Sarissa? The only downside is OP cost, which is negligible as you don't have to pay for as many vents thanks to the kinetic damage being free.
There’s more than one downside.
Sarissa don’t benefit from target analysis, ballistic mastery, cyber augmentation or Wolfpack damage bonuses. There’s a few reasons to want to officer a destroyer. You’re stacking officers via mercenary generation, it’s early game, you’re using support doctrine so lower DP cost officer ships give you more SD value on paper, you want an escort destroyer buffed by big escort package bonuses, you want small ships with decent speed for point capture guerrilla tactics or you’re using them as SO ships for some SO swarm.
The OP savings on vents are not as valuable for a medium energy ship which probably ends up needing OP in vents or caps to handle its medium energy.
Sarissa do eventually get sniped, the downsides of CH leading to a 30% replacement rate doom spiral.
Sarissa cannot benefit from escort package and ITU like hammerhead or even Shrike can. Shrike and Sarissa also can’t benefit from BRF.
Hammerhead does not have plasma burn, making it fit more types of fleets than the Shrike does, which requires either very careful micro or a fleet designed for plasma burn to work since the shrike will constantly force itself into danger.
Sarissa and Shrike both not benefitting from AAF, nor having more than 1 light Needler or railgun.
Shrike isn’t exactly the best at hunting down frigates either. When I used Shrikes I felt their best uses were for CH tactics and for aggressive short range tactics. Typically when a Shrike’s attacking a frigate it’s either so weak it doesn’t matter if you hunted it down or annoying enough the shrike struggles to hunt it down; Glimmer, Lux, SO frigates, Wolf. Maybe you could get it to more quickly hunt down frigates with harpoon or gorgons but then that leaves you praying the missiles actually get used against frigates or hoping the frigate doesn’t just avoid the harpoons with pd+backing away. Sabots could be the play instead but then you have to rely on AMB or its medium energy on getting the kill, while the frigate is likely already retreating with its 135+ speed.
The Hammerhead can effectively escort burst mobility ships besides the Nova because escort package boosts its 90 top speed, too. Nova I doubt hammerhead can keep up, I would suggest shrike can’t either but I haven’t tried it, maybe it’ll keep up.
When you say retreat AI you mean specifically the retreat command? That’s such a niche thing relevant to point capture guerrilla tactics or fighter swarm playstyles. For both of them you’d probably benefit from having some slower ships than the hammerhead - like the Heron, Astral or
maybe an Odyssey. I think without system expertise, Hammerhead without escort package would keep an even pace with an Odyssey in long distances. Even if you don’t, both of those tactics should be able to retreat as a group with no issue. Taking a few extra seconds to get out wouldn’t matter unless you’re losing.
If you’re retreating because you’re losing, Shrike would be better at that but I don’t think that’s a valuable trait to single out as an upside for a combat ship.
P.S. I’ve been experimenting with replacing CH Sarissa with elite point defense CH DTA Broadsword or even Gladius. On paper they end up being similar, except +2 DP instead of +3. Not trying to imply anything here besides sharing that weird thought, requires more comparison testing.