RSV has less hull than escorts, even with resists it cannot survive much damage with shield down.
And bleedthrough is not a problem, if you use 2 assimilated set peaces for proc hull heal.
I primarily run an RSV with an Engineering captain... with resists I do quite well with a bare hull actually... rarely have to hit the Eng powers (and choose not to due to the longer cooldowns), but it's there for emergencies (and PvP)
The Fed RSV + Eng captain does a LOT better than my Garumba w/ Tactical that has a lot more hull set up (and more skill pts spent in resists) and has much better evasion capability.
I'm pretty sure that the reason is Huill Regen. In addition to assimilated 2 piece, my Engineering Team can bring me from 2/3 dead back to full health and add another +28 Hull Regen because of my maintanance DOFFs, and can be reused every 15 seconds. The regen would be pointless without good resists keeping the incoming damage low.