I don't know what inept kumari captains you have seen, but it is is far, far from being brittle. I'm currently using the Charal-type on one of my Fed chars (bought it primarily for RP reasons: andorian char, all andorian boff and doff crew) and I'm surprised that it is quite sturdy. when I read all the things about it being made out of paper and being a glass-cannon, I really feared for the worst and that I'd be taking a ship with defensive values of a T3-ship or a basic Aquarius into STFs.
Surprisingly, I was pretty much en par with my Fleet Defiant regarding hitpoints and shield values, while having an additional, defensive boff skill (considering the ensign slot isn't a useless third tac ensign).
Afterwards I looked at the raw stats for each Fed escort and started comparing:
On paper, the Kumari has the same shield mod and more hull than the basic fed escorts and basic raptors (who have more hull, but worse shields) and is on the same level as the c-store Armitage and just slightly worse than the Fleet Defiant, who is burdened with a third Tac-Ensign.
Fleet Defiant: 33.000 Hull, 0.9 Shield Mod
Armitage: 32.000 Hull, 0.9 Shield Mod
Kumari: 32.000 Hull, 0.9 Shield Mod
Basic Fedscort*: 30-31.000 Hull, 0.9 Shield Mod
The Charal looks to be the best out of the bunch and on par with other escorts. Its probably the other versions I see going boom habitually but I can't be sure since I don't ask and can't tell the difference just by looking. Speed would definitely help the other versions as well as the Birds of Prey.