You still can't give bosses too much randomness, there needs to be a level of scripting. You don't want to have your damage buffs go to waste because RNG said so, causing you to potentially hit the enrage as well, this is bad RNG. Make hard hitting raid-AoE random and you can no longer reliably use Blood for Blood at any point in the fight.

T10 is a good example of a fight where randomness is done well and is a good base from where to improve.