One of the main problems is how the formula is always the same.

Boss hits tank. Boss does tank buster. Boss does unavoidable AoE. Repeat.
Avoidable AoE is sprinkled on the ground, acting almost as a death sentence.

Also, knockoff edge instant kill AoE is boring and extremely lazy.

There is very little persistent damage that has to be watched out for, everything that isn't avoidable is just a burst. Throw out some mechanics where a few players have to manage stacking DoTs.

There could be a mechanic that requires an add to be tanked by DPS that gives a debuff. When the add dies, the player with threat gets nuked, amplified by stacks. Requiring the off tank to pick up the add before it dies, but not too soon or the tank will get too many stacks and die.