Stagger is basically effective health; the only RNG is how good you are at purifying. The PB mechanic also lets us decide when we want the most mitigation (pop PB right before you know you'll take a big hit). WOWhead is being slow today but I do believe our passive damage reduction from Ox Stance is significantly larger than other classes'. It seems likely to me that, if you compare the initial spike damage from a staggered hit to the size of a hit a normal tank takes, we actually take smaller hits than the other tanks. That's balanced out by the increased damage overall from the stagger DOT. We do end up taking more damage than other tanks, but we take smaller initial hits. Tanks die from big hits, not from consistent small ticks.The problem is more baseline numbers. The idea is that monks take damage "smoothly", but take more overall to compensate. The problem is since the nerfs to energy regen and baseline stagger, monks actually take the most burst damage out of any tank on top of taking the most overall damage. The only way to make up for that is with self-healing and avoidance (both of which are higher than average), but both of those are highly RNG-dependant mechanics
As for RNG on Elusive Brew - every tank has this to some extent in their active mitigation. Ask Druids about Savage Defense.
Dodge from Agility stacking+20%parry from Shuffle+5% parry from swift reflexes+30% from Elusive Brew means with our AM up we'll be at around 70-80% (depending on how much Dodge we get from Agility). At that point, it stops being RNG and starts being a pretty good bet. Yeah, we'll still get smashed sometimes, but the chance of multiple hits getting through our avoidance (what actually kills tanks) is pretty low. Even without EB we'll be at around 35% passive avoidance even in crap gear. That's...pretty good.
So overall, what's the tradeoff for Brewmasters?
Pros - we still take smaller (initial) hits than the other tanks, and we take fewer of them thanks to high avoidance.
Cons - we end up taking more overall damage, and our EH/Avoidance are much more dependent on player skill than other tanks.
Yes, nerfs hurt, but they put us where every other tank is at - you have little or no room to use anything but your active mitigation skills, so you have to make a choice between AM and more DPS.