Really, the loot is random. It just sucks. What we're feeling is the ticking of the clock and the desire to have our gear ASAP, not a weighted loot system.

If you're confused, know this: Ever piece of loot has the same chance of dropping at any single drop, and the chances are "reset" after each pull. Just because an item was dropped once doesn't mean that the chances of the next drop have changed from the first time.

That being said, the past 5 EX dungeons runs haven't dropped a single healer piece for me. That's life.