Your list is a lot more shooty than choppy, other than the Guard who have a massive bullesye over their head.
I'd say you'd get more out of your preds and devs rerolls 1s to wound all game than than maybe getting to rez 1 guard before they die.
And DC do 2 things I've found DBH.
They aren't durable at all as you mentioned, the 6+++ is mostly a joke, though they hit pretty hard, but what they have in spades is *disruption*.
Forlorn Fury a squad up if you go first is absolutely insane most games.
My list runs 1 for that, kept cheap with chainswords and hand flamers, purely to gum up the works of my opponents plans and either kill a bunch of infantry screen, or tie up shooting units.
But that idea works because I also have ccw
scout squads doing the same, along with aggressively moved scout and attack bikes, and a libby dread with wings, all putting pressure on the opponent and keeping him from getting out of his deployment zone.
The 2nd thing DC excel at is using Descent of Angels with Lemartes backing them up.
I run a unit of 8 with 3 hammers, rest chainswords and bolters.
Turn 2 they drop in and kill something very reliably, and try to tri lock something to avoid the return fire, while my smash captain usually also nukes something turn 2 after he spent turn 1 screened behind all the scouts and bikes.
So they can do a lot of work, but if you just try to jump them up the board they die way to easy.
They're basically a smash captain, but in unit form, a 1 and done missile