This is mostly a WHM problem. Also your lowered iLv is a HUGE factor as well (as well as his gear and CDs) it makes a world of difference. Ive tested this with friends, and using gear from the prior dungeon, vs gear from ABOVE the dungeon, and its a night and day difference (ppl will argue otherwise). spamming cure2 is NOT enough to keep a tank alive with gear prior to the dungeons gear. you MUST weave oGCDs, and they MUST use CDs. (And WHM will run into problems eventually, too many unlucky crits, having to dodge or die, DPS take too long to kill, etc)
AST and SCH handle it much better being able to weave in more oGCDs. (testing the same tank, same gear, same CD usage from the tank, and comparing) but lilies do make it much easier, and WHMs oGCDs above 50 also really help a ton.
WHMs primary saving grace is its holy stun, but its FAR more reliant on the groups DPS, its easy for you to run out of oGCDs to weave, and the tank to run out of CDs if the enemy isnt dead in a reasonable amount of time. (Ive seen tanks full pull all mobs in aurum vale while im WHM, and im like, i have no oGCDs, i spam cure2, and my "run out of MP faster" oGCD. (PoM) half way into the fight, im always out of MP.)
But if you have the gear from the NEXT dungeon (higher iLv is better, the sync iLv is above the dungeons drop gear) you'll notice how much easier it is to keep a tank up with cure2 spam, and no oGCD weaved. (exception being 3+ packs, you still need to weave, but its far easier) Weapon of course making a pretty big difference, in comparison to the MND of armor/accessories.