Hi once again,
Castellan vs Cobra:
4+ armour vs 5+ armour
+1 battery + 15cm range
+ missile range
+1 turret
-5cm speed
is worth 20pts to me.

The armour is a biggie. The Range and missiles as well. Really, you'd learn to love this vessel.
Better match is versus the Infidel:
same armour, +1 turrets, boarding torps vs missiles, -10cm speed, +15cm range.
Warden, yes 5pts warranted. 5cm means it can overtake the Custodian. So I can keep it a little further back.
I can present an abeam target to shoot with 1 lance, which is better then 2 batteries.
Look, I have my flying hours with this Castellan and Warden and I would not, never, increase them in strength. Nor lower points.
Perhaps you think on paper that they look perhaps a lesser choice but they truly aren't. They can win games. (From experience...).
ps the 4RG Warden variant for 25pts would be cute to be honest.
edit:
Firewarriors on the shipsSince the ships in the draft all have firewarrariors aboard to get normal boarding values what is the status of Merchants, Heroes and Explorers taken in this fleet. In a joint fleet operation I can see Firewarriors stationed on all vessels. Would it be an idea to add Firewarriors to mentioned ships for +15pts if a Kor'O & Custodian is present?
If Firewarriors was dropped completely I would have nu qualms about it either.