I would like to disagree, most of the damage inflicted on a tank should be via guard, meaning it bypasses your defenses anyway.
Big white hitters:
Sniper: Ambush, Snipe, Takedown, Followthrough (30-40m abilities!) +Series of Shots (channeled)
Beside Snipe nothing can autocrit.
I run a 31/1/9 tankshadow in dps gear when protecting healer (~22k life with endu stim), and do not feel squishy at all.
Always fun to see RESIST pop up after a jugger tried to smash me.
I know about all the big white damage attacks and I know only Snipe has an auto crit built in but will anything the crits anyway still by pass a shield? Gunslingers and Snipers with 30% crit chance form gear plus 5% for their buff and 4% talented in Snipe/Charged Burst, Series of Shots/Speed Shot and Followthrough/Trick Shot at 39% crit chance. Those are all hard hitters on your list and if they are going to by pass a shield ~40% of the time would you be better off with the higher DPS of a focus?