Also please note that blizzard has also adopted a similiar model example, 5.0, 5.2, 5.4 - Raid content whilst 5.1 and 5.3 were simply casual content patches.
Blizzard give you at least an average of 10 Bosses per Raid-Tier (if not even more), huge raid instances and 2 difficulty settings to progress in. (not counting lfr)

What do we have here? 4 Bosses for how much longer?
Nowadays this is not acceptable.