Not a WAR, but I talk a lot with my war who does some pretty sick Deeps in T11.

You can turn Defiance off in the last phase right after the tank swap mechanic and you don't have to turn it back on until the bosses first action after Nanospore jet (If he fires the rockets or if he starts Nerve gas, you need to turn defiance back on then).

As for people dying to resonance, no that almost never happens. Your healers may be having a problem?