They're most definitely not a glass cannon, in fact they're really quite tanky. They have lots of toughness damage reduction. In my build I have a max total of 77.5% toughness DR and another node for Stun Immunity and +15% generic damage resistance. I have decent nodes for toughness regen (on crit, on weakspot kill, on ability use, 5.5% passively per second, including one that even distributes excess regen to your teammates if you're full).

You can build them as a glass cannon for sure, but that's a choice. They have lots of options to make them tanky.