PvP is so SILLY to casters that I once saw a Summoner sending his Ifrit to harass the BLM and then the team just IGNORED him because our plan was to down the BLM for last (if there was one). The Ifrit just kept its attacks (ocasional stun included) for the BLM to do NOTHING
I do think they should take back the 100% interruption rate on healers, but it sounds like that BLM was just bad, honestly. Ifrit's normal attacks only go every 4 seconds. He had time either for sleep or Blizzard to heavy it, then sleep. Or use Surecast or Swiftcast? I know in the heat of battle you forget about those things, but he could have also used his BLM 'teleport' ability. =/ BLM shouldn't have an issue at all.

Healers on the other hand, SE needs to give them a break. Except SCH. They're doing fine.