This is just my opinion, no harm intended:

You are right, the tank was getting destroyed in every pull and dealing with people like that is a nightmare. The real problem wasn't tank's gear though, the problem was he didn't know how to use cooldowns properly (off timed CD, no stuns, etc). Honestly that dungeon doesn't help either, the damage taken there is the highest from all dungeons below lvl 70.

That said, you still have a lot to learn about being a healer. You are too slow healing, you don't anticipate tank busters, you don't apply shields between pulls, you don't DPS properly and so on.

It's an accumulation of small things what makes content stressing, not just a undergeared tank. (IMO he's not really undergeared, but it's improvable for sure).