This isn’t new, Tanks pull big according to their cool downs, been like this for several expansions. Tanks have been self-sufficient and still are to a degree. With the nerf to tanks healing this expansion tanks may pull differently in mythic+ but until then expect to see large pulls in heroics. Plus learn to not attack any mobs till the tank stops pulling. Or you will pull aggro, also use your cooldowns on all these big pulls, don’t hold them. I see that a lot.