Council of Elders: This is pretty high constant damage, but on heroic there still are more "burst" phases with more "relaxed" phases of damage.
Megaera: (Relative) downtime (again especially on normal).
Durumu: (Relative) downtime (again, especially on normal).
Yeah, that's 5 of your first 8 bosses with "downtime" phases. Even on heroic mode, of which I've done all but Durumu (and primordius), there are relatively low-damage phases for downtime. I don't understand your point.
This tier honestly has a lot of throughput control and definitely a lot of resource management. When I was healing Council of Elders, on the first few pulls I would be oom as soon as the 4th possession phase. A big challenge of the fight was allocating cooldowns and healing properly so that I would be able to continue dealing with the constant, massive amount of raid damage while taking advantage of relative downtime periods. Part of the challenge there was realizing that while there was almost constant raid damage, only certain raid damage phases were especially deadly, the remaining phases could in fact be "triaged."
I agree that constant "how fast can you spam X" is not fun. But I don't see this in the current tier at all, perhaps you'd like to elaborate?