Do you understand how WAR tank stance works? It's a bit more health and a passive buff to healing recieved. There is no built-in mitigation. Everything does the same amount of damage to a WAR in Defiance that it would do in Deliverance.
And that extra health and healing received would have made all the difference in those cases.

I mean, the "Little bit" of extra health (25%) means it's going to take a few more hits to down you, and the healing received up helps a great deal, it's on par with Convalescence, makes it way easier for the healer to keep you up when you are getting gangbanged by a ludicrous number of mobs because you decided to pull big.

But no, gotta do the biggest possible pulls in DPS stance, doesn't matter if the healer can't keep up without a little extra help.
Cue the epidemic of dead tanks in Levelling Roulette that i experienced back when i was levelling my other classes.
Maybe i'm just unlucky, but it was like some kind of bad running gag.