The difference is not the tanking being more squishy, it has to do with the tweaks on how much ilvl is valued in dungeons.

For example, in HW, if the dungeon said you need to have ilvl 120, then at 120 the mobs would hit decently hard that you would have to heal more, but not have to spam. Like 2 mid/high heals and back to dpsing for a good amount. When you reach ilvl of like 270, you were able to fly through things and not even worry.

Now, in SB, if you need ilvl of 240, then at 240 you would have to really focus on healing. You could expect only time to cast a dots (Damage Over Time Spell) and then back to casting a lot of heals. I bet you that when people are ilvl 320+, you can go back to big pulls and focus more on dpsing than healing.