A little late answer, but better late than never.
About Phase Shunt: solution can be to force AI to deselect their target before using Phase Shunt, and after using it, lock on same or any ship. AI already often doing so, that’s why sometimes it use Phase Shunt correctly and sometimes just put ship’s stern in the way of missiles. I think it can be crucial for balance. Kadur ship is strong in 1 to 1 combat, even sometimes too strong for such fast ships, but in real fight they often get hits at stern because of poor maneuverability. And Phase Shunt potentially can solve it, and make some Kadur ships overpowered, may be.
About corvettes: Yes, I was talking mostly about Myrmidon and Immortal. I found out that they actually have turrets
even some vanilla fighters have one, I never looked so closely, LoL. I have tested corvettes as escort/support for other ships, mostly frigates and destroyers and there are some results:
Phalanx, as I think, supposed to be antimissile/fighter escort corvette. It’s not very effective at that role. Its two fixed Light Railgun Arrays can present a thread only for lightest fighters like Talon or Wasp, it just too weak. Sling ABM also not very good. It can be very effective as antimissile weapon, but only if missiles are flying directly to ship with those systems, they even can protect ship from swarm of unguided missiles. But, if missiles are flying around ship, Sling ABM have hard time shooting them down. Battlescape life of Phalanx corvettes are longer than of other two, mostly because they keep distance to enemy ships and be able to effectively use shields (their weaponry don’t generate much flux). May be, they even don’t need to increase survivability, but firepower must be increased. I think it need 2 Light Railgun Arrays in turrets and antifighter missiles (vanilla, you need 2-3 of them), or 2 Strike Cannons (perhaps not a good choice, Phalanx with them most likely will try to attack bigger ships and will be destroyed).
Main compline with Myrmidons and Immortals are tracking speed of main gun, it’s too slow, can’t compensate maneuvers of corvette and thus, can’t effectively shoot even at destroyers. I think, concept of Myrmidons and Immortals is long rage support craft. In that situation is better to have main gun in fixed mount and turret with antimissile/fighter weapon (they are vulnerable to heavy fighters now), it can be Light Railgun Array or Strike Cannon, or even some vanilla weapon.
Also, did you think about adding flare/active flare launchers to all corvettes?
About drones: I mean using drones like tiny fighters without crew, deploy and support like fighters, if it possible of course.
More about Buzzard, it have same problem as Myrmidons and Immortals, to slow main gun. May be better to give Buzzard special ability “Augmented Turret System”?