Blood craze procs off of crits. If you get crit by a boss in ulduar then instead of eating a 15-20k hit you eat a 30-40k hit... goodluck taking that with any combination of hits, completely randomly throughout the fight. I dont think a tick of blood craze at 100k health would be worth the retarded amounts of damage you would be getting shocked with.
Edit: Just to throw it out there as i quickly read your post the first time. Defense and resil do the same thing by reducing your chance to be crit. 5.6% being the uncritable by bosses level. The difference is that resil lowers how much you are crit for by a percentage and defense rating increases avoidance/mitigation stats. Either way, getting crit by a boss is bad.
"If I'm doing a fight and I need more threat... I try harder. If I'm doing a fight and I need my taunts not to miss, then I wear hit." -Veneretio