Turn 1-3 is mostly just the ability to interrupt. Turn 4 is admittedly a DPS check, which means that what matters most is whether your tank and DPS are geared in a couple ilv90 pieces for that.

Turn 5's HP requirements are just a flat out ilv90 gear check. Basically it requires you have nearly half or more body pieces (since accessories for nontanks dont include vitality) be ilv90.

I wish there were more fights like Twintania and others a bit harder than Turn 4 that weren't mere gear checks.

As it is currently in the game you have only one truly challenging encounter, and that encounter is gear gated to begin with.