Off the top of my head paladin gcd rotation is 1,2,3,4,5,5,5. Then during burst it adds 6,6,6. Then they have oGCDs 7,8,9, 10, 11 to weave through those.
The designers have the philosophy that "healers need to heal" why is it not "tanks need to tank" and fill 90% of their kit with defensives.
Like, the tanks should have at most 4 dps buttons and "the fun" should be from using their extensive mitigation tools to minimize the damage they take and hold aggro. "But what about the casual content where those tools are extremely redundant?" Some may ask. Don't worry, just go play ultimate!