This is normal. Leveling up, at even once you hit level 70 and start gearing up, you'll be squish. Squish af.

You will have to utilize tank stance and keep rotating CD's a lot.

It's only when you start to gear up, with better gear than the dungeons provide, that you'll find yourself being tanky and able to afford to focus more on damage.

It's just part of the way they scale Tanks and Healers. So that while leveling up doing at level content can be rough. But once you start to outgear them they become cakewalks.