Krahta by itself isn’t very good I’d think. Even with the Makuta keyword giving her +2 to her cannon rolls, it’s still a sea monster, although somewhat faster than most. Her main draw is her UT ability, which you could try and spam with friendly ships, to get UT’s as you mentioned.
I feel that the Fallen Angel would be some kind of hybrid, since the Makuta keyword gives her very accurate cannons, and she has lots of cargo space. Looking at her again, I’m wondering if she’s too cheap at 15 points….
Severed Limb is interesting. Good cargo and speed, and okay cannons with some combat oriented abilities. If not for pure brawling, then for some ramming and boarding set ups. Even though it’s less accurate, I’d probably use the grape shot with the middle 3L cannon, to get the little bit of extra range, and the accuracy.